Add test cases

Author: westonruter

src/wp-includes/author-template.php

@@ -89,7 +89,7 @@ function the_author( $deprecated = '', $deprecated_echo = true ) {
  * @since 6.9.0 Added the `$post` parameter. Unknown return value is now explicitly null instead of void.
  *
  * @param int|WP_Post|null $post Optional. Post ID or post object. Default is global `$post` object.
- * @return string|null The author's display name, or null if unknown.
+ * @return string|null The author's display name. Empty string if unknown, or null if no valid post.
  */
 function get_the_modified_author( $post = null ) {
 	$post = get_post( $post );

tests/phpunit/tests/user/getTheModifiedAuthor.php

@@ -64,4 +64,36 @@ public function test_get_the_modified_author_when_post_global_does_not_exist() {
 		$GLOBALS['post'] = null;
 		$this->assertNull( get_the_modified_author() );
 	}
+
+	/**
+	 * @ticket 64104
+	 */
+	public function test_get_the_modified_author_when_invalid_post() {
+		$this->assertNull( get_the_modified_author( -1 ) );
+	}
+
+	/**
+	 * @ticket 64104
+	 */
+	public function test_get_the_modified_author_for_another_post() {
+		$expected_display_name = 'Test Editor';
+
+		$editor_id = self::factory()->user->create(
+			array(
+				'role'         => 'editor',
+				'user_login'   => 'test_editor',
+				'display_name' => $expected_display_name,
+				'description'  => 'test_editor',
+			)
+		);
+
+		$another_post_id = self::factory()->post->create();
+
+		$this->assertSame( '', get_the_modified_author( $another_post_id ) );
+		$this->assertSame( '', get_the_modified_author( get_post( $another_post_id ) ) );
+
+		add_post_meta( $another_post_id, '_edit_last', $editor_id );
+		$this->assertSame( $expected_display_name, get_the_modified_author( $another_post_id ) );
+		$this->assertSame( $expected_display_name, get_the_modified_author( get_post( $another_post_id ) ) );
+	}
 }