diff --git a/package.json b/package.json
index ed5d70e..d36e43f 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "death-notifier",
-    "version": "0.14.10", "_comment_version": "Also update version in `composer.json`!",
+    "version": "0.14.11", "_comment_version": "Also update version in `composer.json`!",
     "description": "Get notified when a famous person dies.",
     "author": "Florine W. Dekker",
     "browser": "dist/bundle.js",
diff --git a/src/main/index.html b/src/main/index.html
index c02442e..ecd63ac 100644
--- a/src/main/index.html
+++ b/src/main/index.html
@@ -56,7 +56,7 @@
                 <a href="./">Click here to return to the main page</a>
             </p>
 
-            <div id="welcome-part" class="grid">
+            <div id="welcome-part" class="grid hidden">
                 <article>
                     <header>
                         <hgroup>
diff --git a/src/main/php/com/fwdekker/deathnotifier/UserManager.php b/src/main/php/com/fwdekker/deathnotifier/UserManager.php
index 974ee1a..259b40e 100644
--- a/src/main/php/com/fwdekker/deathnotifier/UserManager.php
+++ b/src/main/php/com/fwdekker/deathnotifier/UserManager.php
@@ -117,8 +117,7 @@ class UserManager
      */
     private function minutes_until_interval_elapsed(string $timestamp, int $interval): int
     {
-        $minutes_since_timestamp = (new DateTime("@$timestamp"))->diff(new DateTime(), absolute: true)->i;
-        return $interval - $minutes_since_timestamp;
+        return $interval - ((time() - intval($timestamp)) / 60);
     }
 
 
@@ -148,20 +147,6 @@ class UserManager
         });
     }
 
-    /**
-     * Deletes the user with the given UUID.
-     *
-     * @param string $uuid the UUID of the user to delete
-     * @return Response a satisfied `Response` with payload `null`
-     */
-    public function delete_user(string $uuid): Response
-    {
-        $stmt = $this->conn->prepare("DELETE FROM users WHERE uuid=:uuid;");
-        $stmt->bindValue(":uuid", $uuid);
-        $stmt->execute();
-        return Response::satisfied();
-    }
-
     /**
      * Validates a login attempt with the given email address and password.
      *
@@ -175,15 +160,16 @@ class UserManager
         $stmt = $this->conn->prepare("SELECT uuid, password FROM users WHERE email=:email;");
         $stmt->bindValue(":email", $email);
         $stmt->execute();
-        $user = $stmt->fetch();
+        $user = $stmt->fetch(PDO::FETCH_ASSOC);
 
+        // TODO: Expose whether account exists, it's exposed in forgot password anyway
         return $user === false || !password_verify($password, $user["password"])
             ? [Response::unsatisfied("Incorrect combination of email and password.", "password"), null]
             : [Response::satisfied(), $user["uuid"]];
     }
 
     /**
-     * Returns  `true` if and only if a user with the given UUID exists.
+     * Returns `true` if and only if a user with the given UUID exists.
      *
      * @param string $uuid the UUID of the user to check
      * @return bool `true` if and only if a user with the given UUID exists
@@ -218,6 +204,20 @@ class UserManager
             : Response::satisfied($user);
     }
 
+    /**
+     * Deletes the user with the given UUID.
+     *
+     * @param string $uuid the UUID of the user to delete
+     * @return Response a satisfied `Response` with payload `null`
+     */
+    public function delete_user(string $uuid): Response
+    {
+        $stmt = $this->conn->prepare("DELETE FROM users WHERE uuid=:uuid;");
+        $stmt->bindValue(":uuid", $uuid);
+        $stmt->execute();
+        return Response::satisfied();
+    }
+
 
     /**
      * Updates the indicated user's email address.
@@ -229,6 +229,7 @@ class UserManager
      */
     public function set_email(string $uuid, string $email): Response
     {
+        // TODO: Also send message to old email address
         return Database::transaction($this->conn, function () use ($uuid, $email) {
             $stmt = $this->conn->prepare("SELECT EXISTS(SELECT 1 FROM users WHERE uuid=:uuid AND email=:email);");
             $stmt->bindValue(":uuid", $uuid);
@@ -255,46 +256,6 @@ class UserManager
         });
     }
 
-    /**
-     * Resends the email verification email.
-     *
-     * @param string $uuid the UUID of the user to resend the email for
-     * @return Response a satisfied `Response` with payload `null` if the email was sent, or an unsatisfied `Response`
-     * otherwise
-     */
-    public function resend_verify_email(string $uuid): Response
-    {
-        return Database::transaction($this->conn, function () use ($uuid) {
-            $stmt = $this->conn->prepare("SELECT email, email_verification_token, email_verification_token_timestamp
-                                          FROM users
-                                          WHERE uuid=:uuid;");
-            $stmt->bindValue(":uuid", $uuid);
-            $stmt->execute();
-            $user = $stmt->fetch(PDO::FETCH_ASSOC);
-            if ($user["email_verification_token"] === null)
-                return Response::unsatisfied("Your email address is already verified.");
-
-            $minutes_left = $this->minutes_until_interval_elapsed(
-                $user["email_verification_token_timestamp"],
-                self::MINUTES_BETWEEN_VERIFICATION_EMAILS
-            );
-            if ($minutes_left > 0) {
-                return Response::unsatisfied(
-                    "A verification email was sent recently. " .
-                    "Please wait $minutes_left more minute(s) before requesting a new email."
-                );
-            }
-
-            $stmt = $this->conn->prepare("UPDATE users
-                                          SET email_verification_token_timestamp=unixepoch()
-                                          WHERE uuid=:uuid;");
-            $stmt->bindValue(":uuid", $uuid);
-            $stmt->execute();
-
-            return $this->mailer->queue_email(new VerifyEmailEmail($user["email"], $user["email_verification_token"]));
-        });
-    }
-
     /**
      * Verifies an email address with a token.
      *
@@ -312,19 +273,21 @@ class UserManager
             $stmt->bindValue(":email", $email);
             $stmt->bindValue(":token", $token);
             $stmt->execute();
-            $results = $stmt->fetchAll(PDO::FETCH_ASSOC);
-            if (sizeof($results) === 0)
+            $user = $stmt->fetch(PDO::FETCH_ASSOC);
+            if ($user === false)
                 return Response::unsatisfied(
                     "Failed to verify email address. " .
                     "Maybe you already verified your email address?"
                 );
 
             $minutes_remaining = $this->minutes_until_interval_elapsed(
-                $results[0]["email_verification_token_timestamp"],
+                $user["email_verification_token_timestamp"],
                 self::MINUTES_VALID_VERIFICATION
             );
             if ($minutes_remaining < 0)
-                return Response::unsatisfied("This email verification link has expired.");
+                return Response::unsatisfied(
+                    "This email verification link has expired. Log in and request a new verification email."
+                );
 
             $stmt = $this->conn->prepare("UPDATE users SET email_verification_token=null WHERE email=:email;");
             $stmt->bindValue(":email", $email);
@@ -334,6 +297,49 @@ class UserManager
         });
     }
 
+    /**
+     * Resends the email verification email.
+     *
+     * @param string $uuid the UUID of the user to resend the email for
+     * @return Response a satisfied `Response` with payload `null` if the email was sent, or an unsatisfied `Response`
+     * otherwise
+     */
+    public function resend_verify_email(string $uuid): Response
+    {
+        return Database::transaction($this->conn, function () use ($uuid) {
+            $stmt = $this->conn->prepare("SELECT email, email_verification_token, email_verification_token_timestamp
+                                          FROM users
+                                          WHERE uuid=:uuid;");
+            $stmt->bindValue(":uuid", $uuid);
+            $stmt->execute();
+            $user = $stmt->fetch(PDO::FETCH_ASSOC);
+            if ($user === false || $user["email_verification_token"] === null)
+                return Response::unsatisfied("Your email address is already verified.");
+
+            $minutes_left = $this->minutes_until_interval_elapsed(
+                $user["email_verification_token_timestamp"],
+                self::MINUTES_BETWEEN_VERIFICATION_EMAILS
+            );
+            if ($minutes_left > 0) {
+                return Response::unsatisfied(
+                    "A verification email was sent recently. " .
+                    "Please wait $minutes_left more minute(s) before requesting a new email."
+                );
+            }
+
+            $stmt = $this->conn->prepare("UPDATE users
+                                          SET email_verification_token=lower(hex(randomblob(16))),
+                                              email_verification_token_timestamp=unixepoch()
+                                          WHERE uuid=:uuid
+                                          RETURNING email_verification_token;");
+            $stmt->bindValue(":uuid", $uuid);
+            $stmt->execute();
+            $verification_token = $stmt->fetchAll(PDO::FETCH_ASSOC)[0]["email_verification_token"];
+
+            return $this->mailer->queue_email(new VerifyEmailEmail($user["email"], $verification_token));
+        });
+    }
+
     /**
      * Toggles whether the user receives death notifications.
      *
@@ -349,8 +355,8 @@ class UserManager
                                           WHERE uuid=:uuid;");
             $stmt->bindValue(":uuid", $uuid);
             $stmt->execute();
-            $user = $stmt->fetchAll(PDO::FETCH_ASSOC)[0];
-            if ($user["email_verification_token"] !== null)
+            $user = $stmt->fetch(PDO::FETCH_ASSOC);
+            if ($user === false || $user["email_verification_token"] !== null)
                 return Response::unsatisfied("Please verify your email address before enabling notifications.");
 
             $stmt = $this->conn->prepare("UPDATE users SET email_notifications_enabled=:enabled WHERE uuid=:uuid;");
@@ -379,7 +385,7 @@ class UserManager
             $stmt->bindValue(":uuid", $uuid);
             $stmt->execute();
             $user = $stmt->fetch(PDO::FETCH_ASSOC);
-            if (!password_verify($password_old, $user["password"]))
+            if ($user === false || !password_verify($password_old, $user["password"]))
                 return Response::unsatisfied("Incorrect old password.", "password_old");
 
             $stmt = $this->conn->prepare("UPDATE users
@@ -407,12 +413,12 @@ class UserManager
             $stmt = $this->conn->prepare("SELECT password_reset_token_timestamp FROM users WHERE email=:email;");
             $stmt->bindValue(":email", $email);
             $stmt->execute();
-            $results = $stmt->fetchAll(PDO::FETCH_ASSOC);
-            if (sizeof($results) === 0)
+            $user = $stmt->fetch(PDO::FETCH_ASSOC);
+            if ($user === false)
                 return Response::unsatisfied("No account with that email address has been registered.");
 
             $minutes_left = $this->minutes_until_interval_elapsed(
-                $results[0]["password_reset_token_timestamp"],
+                $user["password_reset_token_timestamp"],
                 self::MINUTES_BETWEEN_PASSWORD_RESETS
             );
             if ($minutes_left > 0) {
@@ -452,14 +458,14 @@ class UserManager
             $stmt->bindValue(":email", $email);
             $stmt->bindValue(":token", $token);
             $stmt->execute();
-            $results = $stmt->fetchAll(PDO::FETCH_ASSOC);
-            if (sizeof($results) === 0)
+            $user = $stmt->fetch(PDO::FETCH_ASSOC);
+            if ($user === false)
                 return Response::unsatisfied(
                     "This password reset link is invalid. Maybe you already reset your password?"
                 );
 
             $minutes_remaining = $this->minutes_until_interval_elapsed(
-                $results[0]["password_reset_token_timestamp"],
+                $user["password_reset_token_timestamp"],
                 self::MINUTES_VALID_PASSWORD_RESET
             );
             if ($minutes_remaining < 0)
diff --git a/src/test/php/com/fwdekker/deathnotifier/DatabaseTestCase.php b/src/test/php/com/fwdekker/deathnotifier/DatabaseTestCase.php
index 3fd5d39..925cf3f 100644
--- a/src/test/php/com/fwdekker/deathnotifier/DatabaseTestCase.php
+++ b/src/test/php/com/fwdekker/deathnotifier/DatabaseTestCase.php
@@ -35,7 +35,7 @@ abstract class DatabaseTestCase extends TestCase
     /**
      * @return Mailer the `Mailer` to install the database schema of
      */
-    function getMailer(): Mailer
+    function get_mailer(): Mailer
     {
         return $this->createStub(Mailer::class);
     }
@@ -43,7 +43,7 @@ abstract class DatabaseTestCase extends TestCase
     /**
      * @return TrackingManager the `TrackingManager` to install the database schema of
      */
-    function getTrackingManager(): TrackingManager
+    function get_tracking_manager(): TrackingManager
     {
         return $this->createStub(TrackingManager::class);
     }
@@ -51,7 +51,7 @@ abstract class DatabaseTestCase extends TestCase
     /**
      * @return UserManager the `UserManager` to install the database schema of
      */
-    function getUserManager(): UserManager
+    function get_user_manager(): UserManager
     {
         return $this->createStub(UserManager::class);
     }
@@ -93,6 +93,6 @@ abstract class DatabaseTestCase extends TestCase
         $this->logger = new Logger("DatabaseTestCase");
         $this->database = new Database($this->logger, $db_tmp_file);
 
-        $this->database->auto_install($this->getMailer(), $this->getUserManager(), $this->getTrackingManager());
+        $this->database->auto_install($this->get_mailer(), $this->get_user_manager(), $this->get_tracking_manager());
     }
 }
diff --git a/src/test/php/com/fwdekker/deathnotifier/UserManagerTest.php b/src/test/php/com/fwdekker/deathnotifier/UserManagerTest.php
index d8509dc..a0e28dd 100644
--- a/src/test/php/com/fwdekker/deathnotifier/UserManagerTest.php
+++ b/src/test/php/com/fwdekker/deathnotifier/UserManagerTest.php
@@ -2,8 +2,13 @@
 
 namespace com\fwdekker\deathnotifier;
 
+use com\fwdekker\deathnotifier\mailer\ChangedEmailEmail;
+use com\fwdekker\deathnotifier\mailer\ChangedPasswordEmail;
 use com\fwdekker\deathnotifier\mailer\Mailer;
 use com\fwdekker\deathnotifier\mailer\RegisterEmail;
+use com\fwdekker\deathnotifier\mailer\ResetPasswordEmail;
+use com\fwdekker\deathnotifier\mailer\VerifyEmailEmail;
+use PDO;
 use PHPUnit\Framework\MockObject\MockObject;
 
 
@@ -16,39 +21,119 @@ class UserManagerTest extends DatabaseTestCase
     private Mailer&MockObject $mailer;
 
 
-    public function getUserManager(): UserManager
+    public function get_user_manager(): UserManager
     {
         return new UserManager($this->logger, $this->database->conn, $this->mailer);
     }
 
-
     public function setUp(): void
     {
         $this->mailer = $this->createMock(Mailer::class);
+        $this->mailer->method("queue_email")->willReturn(Response::satisfied());
 
         parent::setUp();
 
-        $this->user_manager = $this->getUserManager();
+        $this->user_manager = $this->get_user_manager();
+    }
+
+
+    /**
+     * Returns the UUID of the given email address.
+     *
+     * @param string $email the email address to return the email verification token of
+     * @return string|null the email verification token of the given email address
+     */
+    private function get_uuid(string $email): ?string
+    {
+        $stmt = $this->database->conn->prepare("SELECT uuid FROM users WHERE email=:email;");
+        $stmt->bindValue(":email", $email);
+        $stmt->execute();
+        $results = $stmt->fetchAll(PDO::FETCH_ASSOC);
+        return empty($results) ? null : $results[0]["uuid"];
+    }
+
+    /**
+     * Returns the email verification token of the given email address.
+     *
+     * @param string $email the email address to return the email verification token of
+     * @return string|null the email verification token of the given email address, or `null` if there is no user with
+     * the given email address
+     */
+    private function get_email_token(string $email): ?string
+    {
+        $stmt = $this->database->conn->prepare("SELECT email_verification_token FROM users WHERE email=:email;");
+        $stmt->bindValue(":email", $email);
+        $stmt->execute();
+        $results = $stmt->fetchAll(PDO::FETCH_ASSOC);
+        return empty($results) ? null : $results[0]["email_verification_token"];
+    }
+
+    /**
+     * Changes the timestamp of the email verification token of the given email address, if a user with that email
+     * address exists.
+     *
+     * @param string $email the email address to set the timestamp of
+     * @param int $timestamp the timestamp to set
+     */
+    private function set_email_token_timestamp(string $email, int $timestamp): void
+    {
+        $stmt = $this->database->conn->prepare("UPDATE users
+                                                SET email_verification_token_timestamp=:timestamp
+                                                WHERE email=:email;");
+        $stmt->bindValue(":email", $email);
+        $stmt->bindValue(":timestamp", $timestamp);
+        $stmt->execute();
+    }
+
+    /**
+     * Returns the password verification token of the given email address.
+     *
+     * @param string $email the email address to return the password verification token of
+     * @return string|null the password verification token of the given email address, or `null` if there is no user
+     * with the given email address
+     */
+    private function get_password_token(string $email): ?string
+    {
+        $stmt = $this->database->conn->prepare("SELECT password_reset_token FROM users WHERE email=:email;");
+        $stmt->bindValue(":email", $email);
+        $stmt->execute();
+        $results = $stmt->fetchAll(PDO::FETCH_ASSOC);
+        return empty($results) ? null : $results[0]["password_reset_token"];
+    }
+
+    /**
+     * Changes the timestamp of the password verification token of the given email address, if a user with that email
+     * address exists.
+     *
+     * @param string $email the email address to set the timestamp of
+     * @param int $timestamp the timestamp to set
+     */
+    private function set_password_token_timestamp(string $email, int $timestamp): void
+    {
+        $stmt = $this->database->conn->prepare("UPDATE users
+                                                SET password_reset_token_timestamp=:timestamp
+                                                WHERE email=:email;");
+        $stmt->bindValue(":email", $email);
+        $stmt->bindValue(":timestamp", $timestamp);
+        $stmt->execute();
     }
 
 
     public function test_register_user_returns_an_unsatisfied_response_if_the_email_is_used(): void
     {
-        $this->mailer->method("queue_email")->willReturn(Response::satisfied());
-        $this->user_manager->register_user("test@test.test", "password");
+        $this->user_manager->register_user("john@example.com", "password");
 
-        $response = $this->user_manager->register_user("test@test.test", "password");
+        $response = $this->user_manager->register_user("john@example.com", "password");
 
         self::assertFalse($response->satisfied);
     }
 
-    public function test_register_user_returns_a_satisfied_response_if_the_email_is_unused(): void
+    public function test_register_user_registers_the_user_and_returns_a_satisfied_response_if_the_email_is_unused(): void
     {
-        $this->mailer->method("queue_email")->willReturn(Response::satisfied());
-
-        $response = $this->user_manager->register_user("test@test.test", "password");
+        $response = $this->user_manager->register_user("john@example.com", "password");
 
         self::assertTrue($response->satisfied);
+        self::assertNotNull($this->get_uuid("john@example.com"));
     }
 
     public function test_register_user_sends_an_email_with_the_verification_token(): void
@@ -56,11 +141,527 @@ class UserManagerTest extends DatabaseTestCase
         $this->mailer
             ->expects($this->once())
             ->method("queue_email")
-            ->with($this->callback(fn($email) => $email instanceof RegisterEmail && $email->recipient === "test@test.test"))
-            ->willReturn(Response::satisfied());
+            ->with($this->callback(
+                fn($email) => $email instanceof RegisterEmail && $email->recipient === "john@example.com")
+            );
 
-        $response = $this->user_manager->register_user("test@test.test", "password");
+        $response = $this->user_manager->register_user("john@example.com", "password");
 
         self::assertTrue($response->satisfied);
     }
+
+
+    public function test_check_login_returns_an_unsatisfied_response_if_the_email_does_not_exist(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+
+        $response = $this->user_manager->check_login("lydia@other.example.com", "password");
+
+        self::assertFalse($response[0]->satisfied);
+        self::assertNull($response[1]);
+    }
+
+    public function test_check_login_returns_an_unsatisfied_response_if_the_email_is_incorrect(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+
+        $response = $this->user_manager->check_login("lydia@other.example.com", "password");
+
+        self::assertFalse($response[0]->satisfied);
+        self::assertNull($response[1]);
+    }
+
+    public function test_check_login_returns_a_satisfied_response_if_the_email_and_password_are_correct(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+
+        $response = $this->user_manager->check_login("john@example.com", "password");
+
+        self::assertTrue($response[0]->satisfied);
+        self::assertNotNull($response[1]);
+    }
+
+
+    public function test_user_exists_returns_false_if_the_user_does_not_exist(): void
+    {
+        self::assertFalse($this->user_manager->user_exists("invalid-uuid"));
+    }
+
+    public function test_user_exists_returns_true_if_the_user_exists(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        self::assertTrue($this->user_manager->user_exists($uuid));
+    }
+
+
+    public function test_get_user_returns_a_satisfied_response_with_the_user_data_if_the_uuid_exists(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $response = $this->user_manager->get_user($uuid);
+
+        self::assertTrue($response->satisfied);
+        self::assertArrayHasKey("email", $response->payload);
+    }
+
+    public function test_get_user_returns_an_unsatisfied_response_if_the_uuid_does_not_exist(): void
+    {
+        $response = $this->user_manager->get_user("invalid-uuid");
+
+        self::assertFalse($response->satisfied);
+    }
+
+
+    public function test_delete_user_deletes_the_user_and_returns_a_satisfied_response_if_the_uuid_is_used(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $response = $this->user_manager->delete_user($uuid);
+
+        self::assertTrue($response->satisfied);
+        self::assertFalse($this->user_manager->user_exists($uuid));
+    }
+
+    public function test_delete_user_returns_a_satisfied_response_even_if_the_user_was_already_deleted(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+        $this->user_manager->delete_user($uuid);
+
+        $response = $this->user_manager->delete_user($uuid);
+
+        self::assertTrue($response->satisfied);
+    }
+
+    public function test_delete_user_returns_a_satisfied_response_even_if_the_uuid_does_not_exist(): void
+    {
+        $response = $this->user_manager->delete_user("invalid-uuid");
+
+        self::assertTrue($response->satisfied);
+    }
+
+
+    public function test_set_email_returns_an_unsatisfied_response_if_the_email_is_not_different(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $response = $this->user_manager->set_email($uuid, "john@example.com");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_set_email_returns_an_unsatisfied_response_if_the_email_is_already_used(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->user_manager->register_user("lydia@other.example.com", "another-password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $response = $this->user_manager->set_email($uuid, "lydia@other.example.com");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_set_email_returns_a_satisfied_response_and_sends_an_email_if_the_email_is_unused(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $this->mailer
+            ->expects($this->once())
+            ->method("queue_email")
+            ->with($this->callback(
+                fn($email) => $email instanceof ChangedEmailEmail && $email->recipient === "lydia@other.example.com")
+            );
+        $response = $this->user_manager->set_email($uuid, "lydia@other.example.com");
+
+        self::assertTrue($response->satisfied);
+        self::assertNull($this->get_email_token("john@example.com"));
+        self::assertNotNull($this->get_email_token("lydia@other.example.com"));
+    }
+
+    public function test_set_email_retains_the_uuid_of_the_user(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $old_uuid = $this->get_uuid("john@example.com");
+
+        $this->user_manager->set_email($old_uuid, "lydia@other.example.com");
+        $new_uuid = $this->get_uuid("lydia@other.example.com");
+
+        self::assertEquals($old_uuid, $new_uuid);
+    }
+
+    public function test_set_email_disallows_logging_in_with_the_old_email_address(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $this->user_manager->set_email($uuid, "lydia@other.example.com");
+
+        self::assertFalse($this->user_manager->check_login("john@example.com", "password")[0]->satisfied);
+    }
+
+
+    public function test_verify_email_returns_an_unsatisfied_response_if_the_email_does_not_exist(): void
+    {
+        $response = $this->user_manager->verify_email("does-not-exist@example.com", "token");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_verify_email_returns_an_unsatisfied_response_if_the_wrong_token_is_given(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+
+        $response = $this->user_manager->verify_email("john@example.com", "incorrect-token");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_verify_email_returns_an_unsatisfied_response_if_an_email_is_already_verified(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $token = $this->get_email_token("john@example.com");
+
+        $this->user_manager->verify_email("john@example.com", $token);
+        $response = $this->user_manager->verify_email("john@example.com", $token);
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_verify_email_returns_an_unsatisfied_response_if_the_token_is_expired(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_email_token_timestamp("john@example.com", "1640995200");
+        $token = $this->get_email_token("john@example.com");
+
+        $response = $this->user_manager->verify_email("john@example.com", $token);
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_verify_email_verifies_the_email_and_returns_a_satisfied_response_if_the_verification_token_is_valid(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+        $token = $this->get_email_token("john@example.com");
+
+        $response = $this->user_manager->verify_email("john@example.com", $token);
+
+        self::assertTrue($response->satisfied);
+        self::assertNull($this->get_email_token("john@example.com"));
+        self::assertTrue($this->user_manager->get_user($uuid)->payload["email_verified"] === 1);
+    }
+
+
+    public function test_resend_verify_email_returns_an_unsatisfied_response_if_the_uuid_does_not_exist(): void
+    {
+        $response = $this->user_manager->resend_verify_email("invalid-uuid");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_resend_verify_email_does_not_send_an_email_and_returns_an_unsatisfied_response_if_the_email_is_already_verified(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+        $token = $this->get_email_token("john@example.com");
+        $this->user_manager->verify_email("john@example.com", $token);
+
+        $this->mailer->expects($this->never())->method("queue_email");
+        $response = $this->user_manager->resend_verify_email($uuid);
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_resend_verify_email_does_not_send_an_email_and_returns_an_unsatisfied_response_if_the_user_recently_registered(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $this->mailer->expects($this->never())->method("queue_email");
+        $response = $this->user_manager->resend_verify_email($uuid);
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_resend_verify_email_does_not_send_an_email_and_returns_an_unsatisfied_response_if_an_email_was_recently_sent(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_email_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_VERIFICATION_EMAILS + 1)
+        );
+        $uuid = $this->get_uuid("john@example.com");
+        $this->user_manager->resend_verify_email($uuid);
+
+        $this->mailer->expects($this->never())->method("queue_email");
+        $response = $this->user_manager->resend_verify_email($uuid);
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_resend_verify_email_sends_an_email_and_returns_a_satisfied_response_if_no_email_was_recently_sent(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_email_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_VERIFICATION_EMAILS + 1)
+        );
+        $uuid = $this->get_uuid("john@example.com");
+
+        $this->mailer
+            ->expects($this->once())
+            ->method("queue_email")
+            ->with($this->callback(
+                fn($email) => $email instanceof VerifyEmailEmail && $email->recipient === "john@example.com")
+            );
+        $response = $this->user_manager->resend_verify_email($uuid);
+
+        self::assertTrue($response->satisfied);
+    }
+
+    public function test_resend_verify_email_disallows_verifying_the_email_with_the_old_token(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $old_token = $this->get_email_token("john@example.com");
+        $this->set_email_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_VERIFICATION_EMAILS + 1)
+        );
+        $uuid = $this->get_uuid("john@example.com");
+        $this->user_manager->resend_verify_email($uuid);
+
+        $response = $this->user_manager->verify_email("john@example.com", $old_token);
+
+        self::assertFalse($response->satisfied);
+    }
+
+
+    public function test_toggle_notifications_returns_an_unsatisfied_response_if_the_uuid_does_not_exist(): void
+    {
+        $response = $this->user_manager->toggle_notifications("invalid-uuid");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_toggle_notifications_does_not_toggle_notifications_and_returns_an_unsatisfied_response_if_the_email_is_not_verified(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $response = $this->user_manager->toggle_notifications($uuid);
+
+        self::assertFalse($response->satisfied);
+        self::assertTrue($this->user_manager->get_user($uuid)->payload["email_notifications_enabled"] === 1);
+    }
+
+    public function test_toggle_notifications_enables_notifications_and_returns_a_satisfied_response_if_they_are_disabled(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+        $token = $this->get_email_token("john@example.com");
+        $this->user_manager->verify_email("john@example.com", $token);
+
+        $this->user_manager->toggle_notifications($uuid);
+        $response = $this->user_manager->toggle_notifications($uuid);
+
+        self::assertTrue($response->satisfied);
+        self::assertTrue($this->user_manager->get_user($uuid)->payload["email_notifications_enabled"] === 1);
+    }
+
+    public function test_toggle_notifications_disables_notifications_and_returns_a_satisfied_response_if_they_are_enabled(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+        $token = $this->get_email_token("john@example.com");
+        $this->user_manager->verify_email("john@example.com", $token);
+
+        $response = $this->user_manager->toggle_notifications($uuid);
+
+        self::assertTrue($response->satisfied);
+        self::assertFalse($this->user_manager->get_user($uuid)->payload["email_notifications_enabled"] === 1);
+    }
+
+
+    public function test_set_password_returns_an_unsatisfied_response_if_the_uuid_does_not_exist(): void
+    {
+        $response = $this->user_manager->set_password("invalid_uuid", "old-password", "new-password");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_set_password_returns_an_unsatisfied_response_if_the_old_password_is_incorrect(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $response = $this->user_manager->set_password($uuid, "wrong-password", "new-password");
+
+        self::assertFalse($response->satisfied);
+        self::assertFalse($this->user_manager->check_login("john@example.com", "new-password")[0]->satisfied);
+    }
+
+    public function test_set_password_sends_an_email_and_returns_a_satisfied_response_if_the_old_password_is_correct(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $uuid = $this->get_uuid("john@example.com");
+
+        $this->mailer
+            ->expects($this->once())
+            ->method("queue_email")
+            ->with($this->callback(
+                fn($email) => $email instanceof ChangedPasswordEmail && $email->recipient === "john@example.com")
+            );
+        $response = $this->user_manager->set_password($uuid, "password", "new-password");
+
+        self::assertTrue($response->satisfied);
+        self::assertTrue($this->user_manager->check_login("john@example.com", "new-password")[0]->satisfied);
+    }
+
+    public function test_set_password_disallows_resetting_the_password_with_an_old_token(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_password_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_PASSWORD_RESETS + 1)
+        );
+        $this->user_manager->send_password_reset("john@example.com");
+        $uuid = $this->get_uuid("john@example.com");
+        $token = $this->get_password_token("john@example.com");
+
+        $this->user_manager->set_password($uuid, "password", "new-password");
+        $response = $this->user_manager->reset_password("john@example.com", $token, "newer-password");
+
+        self::assertFalse($response->satisfied);
+        self::assertFalse($this->user_manager->check_login("john@example.com", "newer-password")[0]->satisfied);
+    }
+
+
+    public function test_send_password_reset_returns_an_unsatisfied_response_if_the_email_does_not_exist(): void
+    {
+        $response = $this->user_manager->send_password_reset("invalid@example.com");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_send_password_reset_does_not_send_an_email_and_returns_an_unsatisfied_response_if_the_user_recently_registered(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+
+        $this->mailer->expects($this->never())->method("queue_email");
+        $response = $this->user_manager->send_password_reset("john@example.com");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_send_password_reset_does_not_send_an_email_and_returns_an_unsatisfied_response_if_an_email_was_recently_sent(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_password_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_PASSWORD_RESETS + 1)
+        );
+        $this->user_manager->send_password_reset("john@example.com");
+
+        $this->mailer->expects($this->never())->method("queue_email");
+        $response = $this->user_manager->send_password_reset("john@example.com");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_send_password_reset_sends_an_email_and_returns_a_satisfied_response_if_no_email_was_recently_sent(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_password_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_PASSWORD_RESETS + 1)
+        );
+
+        $this->mailer
+            ->expects($this->once())
+            ->method("queue_email")
+            ->with($this->callback(
+                fn($email) => $email instanceof ResetPasswordEmail && $email->recipient === "john@example.com")
+            );
+        $response = $this->user_manager->send_password_reset("john@example.com");
+
+        self::assertTrue($response->satisfied);
+    }
+
+    public function test_send_password_reset_disallows_resetting_the_password_with_the_old_token(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_password_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_PASSWORD_RESETS + 1)
+        );
+        $this->user_manager->send_password_reset("john@example.com");
+        $old_token = $this->get_password_token("john@example.com");
+        $this->set_password_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_PASSWORD_RESETS + 1)
+        );
+        $this->user_manager->send_password_reset("john@example.com");
+
+        $response = $this->user_manager->reset_password("john@example.com", $old_token, "password-new");
+
+        self::assertFalse($response->satisfied);
+    }
+
+
+    public function test_reset_password_returns_an_unsatisfied_response_if_the_email_does_not_exist(): void
+    {
+        $response = $this->user_manager->reset_password("does-not-exist@example.com", "token", "new-password");
+
+        self::assertFalse($response->satisfied);
+    }
+
+    public function test_reset_password_does_not_change_the_password_and_returns_an_unsatisfied_response_if_the_wrong_token_is_given(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+
+        $response = $this->user_manager->reset_password("john@example.com", "incorrect-token", "new-password");
+
+        self::assertFalse($response->satisfied);
+        self::assertFalse($this->user_manager->check_login("john@example.com", "new-password")[0]->satisfied);
+    }
+
+    public function test_reset_password_does_not_change_the_password_and_returns_an_unsatisfied_response_if_the_token_is_expired(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_password_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_PASSWORD_RESETS + 1)
+        );
+        $this->user_manager->send_password_reset("john@example.com");
+        $this->set_password_token_timestamp("john@example.com", "1640995200");
+        $token = $this->get_password_token("john@example.com");
+
+        $response = $this->user_manager->reset_password("john@example.com", $token, "new-password");
+
+        self::assertFalse($response->satisfied);
+        self::assertFalse($this->user_manager->check_login("john@example.com", "new-password")[0]->satisfied);
+    }
+
+    public function test_reset_password_changes_the_password_if_the_verification_token_is_valid(): void
+    {
+        $this->user_manager->register_user("john@example.com", "password");
+        $this->set_password_token_timestamp(
+            "john@example.com",
+            time() - 60 * (UserManager::MINUTES_BETWEEN_PASSWORD_RESETS + 1)
+        );
+        $this->user_manager->send_password_reset("john@example.com");
+        $token = $this->get_password_token("john@example.com");
+
+        $response = $this->user_manager->reset_password("john@example.com", $token, "new-password");
+
+        self::assertTrue($response->satisfied);
+        self::assertNull($this->get_password_token("john@example.com"));
+        self::assertTrue($this->user_manager->check_login("john@example.com", "new-password")[0]->satisfied);
+    }
 }
diff --git a/src/test/php/com/fwdekker/deathnotifier/validator/IsEmailRuleTest.php b/src/test/php/com/fwdekker/deathnotifier/validator/IsEmailRuleTest.php
index b082b76..0816690 100644
--- a/src/test/php/com/fwdekker/deathnotifier/validator/IsEmailRuleTest.php
+++ b/src/test/php/com/fwdekker/deathnotifier/validator/IsEmailRuleTest.php
@@ -30,7 +30,7 @@ class IsEmailRuleTest extends RuleTest
 
         $is_valid = $rule->check(["email" => "example@example.com"], "email");
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     public function test_returns_response_message_if_email_is_invalid(): void
@@ -39,7 +39,7 @@ class IsEmailRuleTest extends RuleTest
 
         $is_valid = $rule->check(["email" => "example.com"], "email");
 
-        $this->assertNotNull($is_valid);
-        $this->assertEquals("Enter a valid email address.", $is_valid->payload["message"]);
+        self::assertNotNull($is_valid);
+        self::assertEquals("Enter a valid email address.", $is_valid->payload["message"]);
     }
 }
diff --git a/src/test/php/com/fwdekker/deathnotifier/validator/IsNotBlankRuleTest.php b/src/test/php/com/fwdekker/deathnotifier/validator/IsNotBlankRuleTest.php
index 64dda58..ab8a718 100644
--- a/src/test/php/com/fwdekker/deathnotifier/validator/IsNotBlankRuleTest.php
+++ b/src/test/php/com/fwdekker/deathnotifier/validator/IsNotBlankRuleTest.php
@@ -30,7 +30,7 @@ class IsNotBlankRuleTest extends RuleTest
 
         $is_valid = $rule->check(["input" => "not-blank"], "input");
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     public function test_returns_response_message_if_input_is_the_empty_string(): void
@@ -39,8 +39,8 @@ class IsNotBlankRuleTest extends RuleTest
 
         $is_valid = $rule->check(["input" => ""], "input");
 
-        $this->assertNotNull($is_valid);
-        $this->assertEquals("Use at least one character.", $is_valid->payload["message"]);
+        self::assertNotNull($is_valid);
+        self::assertEquals("Use at least one character.", $is_valid->payload["message"]);
     }
 
     public function test_returns_response_message_if_input_contains_whitespace_only(): void
@@ -49,7 +49,7 @@ class IsNotBlankRuleTest extends RuleTest
 
         $is_valid = $rule->check(["input" => "   "], "input");
 
-        $this->assertNotNull($is_valid);
-        $this->assertEquals("Use at least one character.", $is_valid->payload["message"]);
+        self::assertNotNull($is_valid);
+        self::assertEquals("Use at least one character.", $is_valid->payload["message"]);
     }
 }
diff --git a/src/test/php/com/fwdekker/deathnotifier/validator/LengthRuleTest.php b/src/test/php/com/fwdekker/deathnotifier/validator/LengthRuleTest.php
index 5235a8b..e631488 100644
--- a/src/test/php/com/fwdekker/deathnotifier/validator/LengthRuleTest.php
+++ b/src/test/php/com/fwdekker/deathnotifier/validator/LengthRuleTest.php
@@ -30,7 +30,7 @@ class LengthRuleTest extends RuleTest
 
         $is_valid = $rule->check(["input" => "a"], "input");
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     public function test_returns_null_if_input_is_exactly_maximum_length(): void
@@ -39,7 +39,7 @@ class LengthRuleTest extends RuleTest
 
         $is_valid = $rule->check(["input" => "123"], "input");
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     public function test_returns_null_if_input_is_strictly_inside_range(): void
@@ -48,7 +48,7 @@ class LengthRuleTest extends RuleTest
 
         $is_valid = $rule->check(["input" => "12"], "input");
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     public function test_returns_not_null_if_input_is_strictly_below_minimum(): void
@@ -57,7 +57,7 @@ class LengthRuleTest extends RuleTest
 
         $is_valid = $rule->check(["input" => ""], "input");
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 
     public function test_returns_not_null_if_input_is_strictly_above_maximum(): void
@@ -66,6 +66,6 @@ class LengthRuleTest extends RuleTest
 
         $is_valid = $rule->check(["input" => "1234"], "input");
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 }
diff --git a/src/test/php/com/fwdekker/deathnotifier/validator/RuleTest.php b/src/test/php/com/fwdekker/deathnotifier/validator/RuleTest.php
index b4fe006..afbb35e 100644
--- a/src/test/php/com/fwdekker/deathnotifier/validator/RuleTest.php
+++ b/src/test/php/com/fwdekker/deathnotifier/validator/RuleTest.php
@@ -37,7 +37,7 @@ abstract class RuleTest extends TestCase
 
         $is_valid = $rule->check(["input" => $this->get_valid_input()], "input");
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     public function test_returns_not_null_if_input_is_invalid(): void
@@ -46,7 +46,7 @@ abstract class RuleTest extends TestCase
 
         $is_valid = $rule->check(["input" => $this->get_invalid_input()], "input");
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 
     public function test_returns_not_null_if_input_is_not_set(): void
@@ -55,7 +55,7 @@ abstract class RuleTest extends TestCase
 
         $is_valid = $rule->check(["input" => $this->get_valid_input()], "does_not_exist");
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 
     public function test_returns_unsatisfied_payload_if_input_is_invalid(): void
@@ -64,8 +64,8 @@ abstract class RuleTest extends TestCase
 
         $is_valid = $rule->check(["input" => $this->get_invalid_input()], "input");
 
-        $this->assertNotNull($is_valid);
-        $this->assertFalse($is_valid->satisfied);
+        self::assertNotNull($is_valid);
+        self::assertFalse($is_valid->satisfied);
     }
 
     public function test_returns_payload_with_overridden_message_if_input_is_invalid(): void
@@ -75,8 +75,8 @@ abstract class RuleTest extends TestCase
 
         $is_valid = $rule->check(["input" => $this->get_invalid_input()], "input");
 
-        $this->assertNotNull($is_valid);
-        $this->assertEquals($override, $is_valid->payload["message"]);
+        self::assertNotNull($is_valid);
+        self::assertEquals($override, $is_valid->payload["message"]);
     }
 
     public function test_returns_payload_with_key_of_invalid_input_if_input_is_invalid(): void
@@ -92,7 +92,7 @@ abstract class RuleTest extends TestCase
             "invalid"
         );
 
-        $this->assertNotNull($is_valid);
-        $this->assertEquals("invalid", $is_valid->payload["target"]);
+        self::assertNotNull($is_valid);
+        self::assertEquals("invalid", $is_valid->payload["target"]);
     }
 }
diff --git a/src/test/php/com/fwdekker/deathnotifier/validator/ValidatorTest.php b/src/test/php/com/fwdekker/deathnotifier/validator/ValidatorTest.php
index d1951e3..b78009a 100644
--- a/src/test/php/com/fwdekker/deathnotifier/validator/ValidatorTest.php
+++ b/src/test/php/com/fwdekker/deathnotifier/validator/ValidatorTest.php
@@ -17,7 +17,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_inputs($inputs, $rule_sets);
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     function test_validate_inputs_returns_null_if_all_inputs_are_valid(): void
@@ -30,7 +30,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_inputs($inputs, $rule_sets);
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     function test_validate_inputs_considers_empty_rule_set_to_always_be_valid(): void
@@ -40,7 +40,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_inputs($inputs, $rule_sets);
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     function test_validate_inputs_returns_not_null_if_at_least_one_rule_is_violated(): void
@@ -53,7 +53,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_inputs($inputs, $rule_sets);
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 
     function test_validate_inputs_returns_first_violation_if_multiple_inputs_are_invalid(): void
@@ -66,8 +66,8 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_inputs($inputs, $rule_sets);
 
-        $this->assertNotNull($is_valid);
-        $this->assertEquals("among", $is_valid->payload["target"]);
+        self::assertNotNull($is_valid);
+        self::assertEquals("among", $is_valid->payload["target"]);
     }
 
     function test_validate_inputs_returns_first_violation_if_one_input_is_invalid_in_multiple_ways(): void
@@ -80,9 +80,9 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_inputs($inputs, $rule_sets);
 
-        $this->assertNotNull($is_valid);
-        $this->assertEquals("among", $is_valid->payload["target"]);
-        $this->assertEquals("Field 'among' required.", $is_valid->payload["message"]);
+        self::assertNotNull($is_valid);
+        self::assertEquals("among", $is_valid->payload["target"]);
+        self::assertEquals("Field 'among' required.", $is_valid->payload["message"]);
     }
 
 
@@ -92,7 +92,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_logged_in($session);
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     function test_validate_logged_in_returns_not_null_if_uuid_is_not_set(): void
@@ -101,7 +101,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_logged_in($session);
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 
 
@@ -111,7 +111,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_logged_out($session);
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 
     function test_validate_logged_out_returns_null_if_uuid_is_not_set(): void
@@ -120,7 +120,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_logged_out($session);
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
 
@@ -131,7 +131,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_token($array, $token);
 
-        $this->assertNull($is_valid);
+        self::assertNull($is_valid);
     }
 
     function test_validate_token_returns_not_null_if_token_is_not_set(): void
@@ -141,7 +141,7 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_token($array, $token);
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 
     function test_validate_token_returns_not_null_if_token_does_not_equal_input(): void
@@ -151,6 +151,6 @@ class ValidatorTest extends TestCase
 
         $is_valid = Validator::validate_token($array, "woof");
 
-        $this->assertNotNull($is_valid);
+        self::assertNotNull($is_valid);
     }
 }