diff --git a/includes/class-admin-settings.php b/includes/class-admin-settings.php
index fd9698b..414b604 100644
--- a/includes/class-admin-settings.php
+++ b/includes/class-admin-settings.php
@@ -279,7 +279,7 @@ public function update_settings() {
 					network_admin_url( 'index.php?page=aspireupdate-settings' )
 				)
 			);
-			exit;
+			! defined( 'AP_RUN_TESTS' ) && exit;
 		}
 	}
 
diff --git a/tests/phpunit/includes/AdminSettings_UnitTestCase.php b/tests/phpunit/includes/AdminSettings_UnitTestCase.php
index b9824ac..5130d95 100644
--- a/tests/phpunit/includes/AdminSettings_UnitTestCase.php
+++ b/tests/phpunit/includes/AdminSettings_UnitTestCase.php
@@ -12,6 +12,13 @@ abstract class AdminSettings_UnitTestCase extends WP_UnitTestCase {
 	 */
 	protected static $option_name = 'aspireupdate_settings';
 
+	/**
+	 * The Slug of the Option's page.
+	 *
+	 * @var string
+	 */
+	protected static $options_page = 'aspireupdate-settings';
+
 	/**
 	 * Deletes settings before each test runs.
 	 *
diff --git a/tests/phpunit/tests/AdminSettings/AdminSettings_UpdateSettingsTest.php b/tests/phpunit/tests/AdminSettings/AdminSettings_UpdateSettingsTest.php
new file mode 100644
index 0000000..cac704a
--- /dev/null
+++ b/tests/phpunit/tests/AdminSettings/AdminSettings_UpdateSettingsTest.php
@@ -0,0 +1,249 @@
+<?php
+/**
+ * Class AdminSettings_UpdateSettingsTest
+ *
+ * @package AspireUpdate
+ */
+
+/**
+ * Tests for Admin_Settings::update_settings()
+ *
+ * @covers \AspireUpdate\Admin_Settings::update_settings
+ */
+class AdminSettings_UpdateSettingsTest extends AdminSettings_UnitTestCase {
+	/**
+	 * Test that settings are not updated when $_POST['_wpnonce'] is not set.
+	 */
+	public function test_should_not_update_settings_when_post_wpnonce_is_not_set() {
+		unset( $_POST['_wpnonce'] );
+		$_POST['option_page']           = self::$option_name;
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$settings = get_site_option( self::$option_name, false );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame(
+			$settings,
+			get_site_option( self::$option_name, false )
+		);
+	}
+
+	/**
+	 * Test that a redirect is not performed when $_POST['_wpnonce'] is not set.
+	 */
+	public function test_should_not_redirect_when_post_wpnonce_is_not_set() {
+		unset( $_POST['_wpnonce'] );
+		$_POST['option_page']           = self::$option_name;
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that settings are not updated when nonce verification fails.
+	 */
+	public function test_should_not_update_settings_when_nonce_verification_fails() {
+		$_POST['_wpnonce']              = 'incorrect_value';
+		$_POST['option_page']           = self::$option_name;
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$settings = get_site_option( self::$option_name, false );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame(
+			$settings,
+			get_site_option( self::$option_name, false )
+		);
+	}
+
+	/**
+	 * Test that a redirect is not performed when nonce verification fails.
+	 */
+	public function test_should_not_redirect_when_nonce_verification_fails() {
+		$_POST['_wpnonce']              = 'incorrect_value';
+		$_POST['option_page']           = self::$option_name;
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that settings are not updated when $_POST['options_page'] is not set.
+	 */
+	public function test_should_not_update_settings_when_post_optionspage_is_not_set() {
+		$_POST['_wpnonce'] = wp_create_nonce( self::$options_page );
+		unset( $_POST['option_page'] );
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$settings = get_site_option( self::$option_name, false );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame(
+			$settings,
+			get_site_option( self::$option_name, false )
+		);
+	}
+
+	/**
+	 * Test that a redirect is not performed when $_POST['options_page'] is not set.
+	 */
+	public function test_should_not_redirect_when_post_optionspage_is_not_set() {
+		$_POST['_wpnonce'] = wp_create_nonce( self::$options_page );
+		unset( $_POST['option_page'] );
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that settings are not updated when $_POST['options_page'] is set to an incorrect value.
+	 */
+	public function test_should_not_update_settings_when_post_optionspage_is_set_to_an_incorrect_value() {
+		$_POST['_wpnonce']              = wp_create_nonce( self::$options_page );
+		$_POST['option_page']           = 'incorrect_value';
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$settings = get_site_option( self::$option_name, false );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame(
+			$settings,
+			get_site_option( self::$option_name, false )
+		);
+	}
+
+	/**
+	 * Test that a redirect is not performed when $_POST['options_page'] is set to an incorrect value.
+	 */
+	public function test_should_not_redirect_when_post_optionspage_is_set_to_an_incorrect_value() {
+		$_POST['_wpnonce']              = wp_create_nonce( self::$options_page );
+		$_POST['option_page']           = 'incorrect_value';
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that settings are not updated when $_POST['aspireupdate_settings'] is not set.
+	 */
+	public function test_should_not_update_settings_when_post_aspireupdatesettings_is_not_set() {
+		$_POST['_wpnonce']    = wp_create_nonce( self::$options_page );
+		$_POST['option_page'] = self::$option_name;
+		unset( $_POST['aspireupdate_settings'] );
+
+		$settings = get_site_option( self::$option_name, false );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame(
+			$settings,
+			get_site_option( self::$option_name, false )
+		);
+	}
+
+	/**
+	 * Test that a redirect is not performed when $_POST['aspireupdate_settings'] is not set.
+	 */
+	public function test_should_not_redirect_when_post_aspireupdatesettings_is_not_set() {
+		$_POST['_wpnonce']    = wp_create_nonce( self::$options_page );
+		$_POST['option_page'] = self::$option_name;
+		unset( $_POST['aspireupdate_settings'] );
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that settings are updated when update requirements are met.
+	 *
+	 * @runInSeparateProcess
+	 * @preserveGlobalState disabled
+	 */
+	public function test_should_update_settings_when_update_requirements_are_met() {
+		$_POST['_wpnonce']              = wp_create_nonce( self::$options_page );
+		$_POST['option_page']           = self::$option_name;
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		delete_site_option( self::$option_name );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+		$actual = get_site_option( self::$option_name, false );
+
+		$this->assertIsArray(
+			$actual,
+			'The settings are not an array.'
+		);
+
+		$this->assertArrayHasKey(
+			'api_host',
+			$actual,
+			'There is no "api_host" setting.'
+		);
+
+		$this->assertSame(
+			// phpcs:ignore WordPress.Security.NonceVerification.Missing
+			$_POST['aspireupdate_settings']['api_host'],
+			$actual['api_host'],
+			'The settings were not updated.'
+		);
+	}
+
+	/**
+	 * Test that a redirect is performed when update requirements are met.
+	 *
+	 * @runInSeparateProcess
+	 * @preserveGlobalState disabled
+	 */
+	public function test_should_redirect_when_update_requirements_are_met() {
+		$_POST['_wpnonce']              = wp_create_nonce( self::$options_page );
+		$_POST['option_page']           = self::$option_name;
+		$_POST['aspireupdate_settings'] = [ 'api_host' => 'the.option.value' ];
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$admin_settings = new AspireUpdate\Admin_Settings();
+		$admin_settings->update_settings();
+
+		$this->assertSame( 1, $redirect->get_call_count() );
+	}
+}