diff --git a/tests/phpunit/tests/functions.php b/tests/phpunit/tests/functions.php
index d9e3d5fbb8..f8da780b29 100644
--- a/tests/phpunit/tests/functions.php
+++ b/tests/phpunit/tests/functions.php
@@ -1451,4 +1451,42 @@ class Tests_Functions extends WP_UnitTestCase {
 
 		);
 	}
+
+	/**
+	 * Test stream URL validation.
+	 *
+	 * @dataProvider data_test_wp_is_stream
+	 *
+	 * @param string $path     The resource path or URL.
+	 * @param bool   $expected Expected result.
+	 */
+	public function test_wp_is_stream( $path, $expected ) {
+		$this->assertSame( $expected, wp_is_stream( $path ) );
+	}
+
+	/**
+	 * Data provider for stream URL validation.
+	 *
+	 * @return array {
+	 *     @type array $0... {
+	 *         @type string $0 The resource path or URL.
+	 *         @type bool   $1 Expected result.
+	 *     }
+	 * }
+	 */
+	public function data_test_wp_is_stream() {
+		return array(
+			// Legitimate stream examples.
+			array( 'https://example.com', true ),
+			array( 'ftp://example.com', true ),
+			array( 'file:///path/to/some/file', true ),
+			array( 'php://some/php/file.php', true ),
+
+			// Non-stream examples.
+			array( 'fakestream://foo/bar/baz', false ),
+			array( '../../some/relative/path', false ),
+			array( 'some/other/relative/path', false ),
+			array( '/leading/relative/path', false ),
+		);
+	}
 }