diff --git a/tests/phpunit/tests/functions/wpGetUpdatePhpUrl.php b/tests/phpunit/tests/functions/wpGetUpdatePhpUrl.php
new file mode 100644
index 0000000000000..67831b35e46a5
--- /dev/null
+++ b/tests/phpunit/tests/functions/wpGetUpdatePhpUrl.php
@@ -0,0 +1,91 @@
+<?php
+
+/**
+ * Tests the wp_get_update_php_url() function.
+ *
+ * @group functions
+ *
+ * @covers ::wp_get_update_php_url
+ */
+class Tests_Functions_WpGetUpdatePhpUrl extends WP_UnitTestCase {
+
+	/**
+	 * Tests that wp_get_update_php_url() returns the default URL.
+	 *
+	 * @ticket 65653
+	 */
+	public function test_wp_get_update_php_url_default() {
+		$this->assertSame( 'https://wordpress.org/support/update-php/', wp_get_update_php_url() );
+	}
+
+	/**
+	 * Tests that wp_get_update_php_url() respects the WP_UPDATE_PHP_URL environment variable.
+	 *
+	 * @ticket 65653
+	 */
+	public function test_wp_get_update_php_url_env_var() {
+		$custom_url = 'https://example.com/update-php/';
+		putenv( 'WP_UPDATE_PHP_URL=' . $custom_url );
+
+		$url = wp_get_update_php_url();
+
+		// Clean up.
+		putenv( 'WP_UPDATE_PHP_URL' );
+
+		$this->assertSame( $custom_url, $url );
+	}
+
+	/**
+	 * Tests that wp_get_update_php_url() respects the wp_update_php_url filter.
+	 *
+	 * @ticket 65653
+	 */
+	public function test_wp_get_update_php_url_filter() {
+		$custom_url = 'https://example.org/custom-php-update/';
+		add_filter(
+			'wp_update_php_url',
+			function () use ( $custom_url ) {
+				return $custom_url;
+			}
+		);
+
+		$url = wp_get_update_php_url();
+
+		$this->assertSame( $custom_url, $url );
+	}
+
+	/**
+	 * Tests that wp_get_update_php_url() falls back to the default URL if an empty string is provided.
+	 *
+	 * @ticket 65653
+	 *
+	 * @dataProvider data_wp_get_update_php_url_empty_fallbacks
+	 *
+	 * @param string $empty_value The empty value to test.
+	 */
+	public function test_wp_get_update_php_url_empty_fallbacks( $empty_value ) {
+		add_filter(
+			'wp_update_php_url',
+			function () use ( $empty_value ) {
+				return $empty_value;
+			}
+		);
+
+		$this->assertSame( 'https://wordpress.org/support/update-php/', wp_get_update_php_url() );
+	}
+
+	/**
+	 * Data provider for test_wp_get_update_php_url_empty_fallbacks().
+	 *
+	 * @return array<string, array{
+	 *     empty_value: string,
+	 * }>
+	 */
+	public function data_wp_get_update_php_url_empty_fallbacks(): array {
+		return array(
+			'empty string' => array( '' ),
+			'null'         => array( null ),
+			'false'        => array( false ),
+		);
+	}
+}