diff --git a/includes/class-themes-screens.php b/includes/class-themes-screens.php
index a993daf3..3370c7ff 100644
--- a/includes/class-themes-screens.php
+++ b/includes/class-themes-screens.php
@@ -92,7 +92,7 @@ public function admin_enqueue_scripts( $hook ) {
 	public function redirect_to_theme_install() {
 
 		$nonce = isset( $_REQUEST['_wpnonce'] ) ? sanitize_text_field( wp_unslash( $_REQUEST['_wpnonce'] ) ) : false;
-		if ( $nonce && ! wp_verify_nonce( $nonce, 'query-themes' ) ) {
+		if ( ! $nonce || ! wp_verify_nonce( $nonce, 'query-themes' ) ) {
 			return;
 		}
 
@@ -105,7 +105,7 @@ public function redirect_to_theme_install() {
 		$admin_settings = Admin_Settings::get_instance();
 		if ( $admin_settings->get_setting( 'enable', false ) ) {
 			wp_safe_redirect( admin_url( 'theme-install.php' ) );
-			exit;
+			! defined( 'AP_RUN_TESTS' ) && exit;
 		}
 	}
 }
diff --git a/tests/phpunit/tests/ThemesScreens/ThemesScreens_RedirectToThemeInstallTest.php b/tests/phpunit/tests/ThemesScreens/ThemesScreens_RedirectToThemeInstallTest.php
new file mode 100644
index 00000000..ae0dac1a
--- /dev/null
+++ b/tests/phpunit/tests/ThemesScreens/ThemesScreens_RedirectToThemeInstallTest.php
@@ -0,0 +1,121 @@
+<?php
+/**
+ * Class ThemesScreens_RedirectToThemeInstallTest
+ *
+ * @package AspireUpdate
+ */
+
+/**
+ * Tests for Themes_Screens::redirect_to_theme_install()
+ *
+ * These tests cause constants to be defined and also occur after headers are sent.
+ * They must run in separate processes and must not preserve global state.
+ *
+ * @runTestsInSeparateProcesses
+ * @preserveGlobalState disabled
+ *
+ * @covers \AspireUpdate\Themes_Screens::redirect_to_theme_install
+ */
+class ThemesScreens_RedirectToThemeInstallTest extends WP_UnitTestCase {
+	/**
+	 * Test that a redirect is not performed when $_REQUEST['_wpnonce'] is not set.
+	 */
+	public function test_should_not_redirect_when_request_wpnonce_is_not_set() {
+		unset( $_REQUEST['_wpnonce'] );
+		$_GET['browse'] = 'favorites';
+		define( 'AP_ENABLE', true );
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$themes_screens = new AspireUpdate\Themes_Screens();
+		$themes_screens->redirect_to_theme_install();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that a redirect is not performed when nonce verification fails.
+	 */
+	public function test_should_not_redirect_when_nonce_verification_fails() {
+		$_REQUEST['_wpnonce'] = 'incorrect_value';
+		$_GET['browse']       = 'favorites';
+		define( 'AP_ENABLE', true );
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$themes_screens = new AspireUpdate\Themes_Screens();
+		$themes_screens->redirect_to_theme_install();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that a redirect is not performed when not viewing an unsupported filter.
+	 */
+	public function test_should_not_redirect_when_not_viewing_an_unsupported_filter() {
+		$_REQUEST['_wpnonce'] = wp_create_nonce( 'query-themes' );
+		$_GET['browse']       = 'some-filter';
+		define( 'AP_ENABLE', true );
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$themes_screens = new AspireUpdate\Themes_Screens();
+		$themes_screens->redirect_to_theme_install();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that a redirect is not performed when AP_ENABLE is false.
+	 */
+	public function test_should_not_redirect_when_ap_enable_is_false() {
+		$_REQUEST['_wpnonce'] = wp_create_nonce( 'query-themes' );
+		$_GET['browse']       = 'favorites';
+		define( 'AP_ENABLE', false );
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$themes_screens = new AspireUpdate\Themes_Screens();
+		$themes_screens->redirect_to_theme_install();
+
+		$this->assertSame( 0, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Test that a redirect is performed when viewing an unsupported filter.
+	 *
+	 * @dataProvider data_unsupported_filters
+	 *
+	 * @param string $filter The unsupported filter.
+	 */
+	public function test_should_redirect_when_viewing_an_unsupported_filter( $filter ) {
+		$_REQUEST['_wpnonce'] = wp_create_nonce( 'query-themes' );
+		$_GET['browse']       = $filter;
+		define( 'AP_ENABLE', true );
+
+		$redirect = new MockAction();
+		add_filter( 'wp_redirect', [ $redirect, 'filter' ] );
+
+		$themes_screens = new AspireUpdate\Themes_Screens();
+		$themes_screens->redirect_to_theme_install();
+
+		$this->assertSame( 1, $redirect->get_call_count() );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public function data_unsupported_filters() {
+		return self::text_array_to_dataprovider(
+			[
+				'favorites',
+			]
+		);
+	}
+}