function injectIntoGetAllFiles(testWindow, extraFilePath) {
        var ProjectManager  = testWindow.brackets.test.ProjectManager,
            FileSystem      = testWindow.brackets.test.FileSystem,
            origGetAllFiles = ProjectManager.getAllFiles;

        spyOn(ProjectManager, "getAllFiles").andCallFake(function () {
            var testResult = new testWindow.$.Deferred();
            origGetAllFiles.apply(ProjectManager, arguments).done(function (result) {
                var dummyFile = FileSystem.getFileForPath(extraFilePath);
                var newResult = result.concat([dummyFile]);
                testResult.resolve(newResult);
            }).fail(function (error) {
                testResult.reject(error);
            });
            return testResult;
        });
    }
Patches ProjectManager.getAllFiles() in the given test window (for just the current it() block) so that it
includes one extra file in its results. The file need not actually exist on disk.
@param {!Window} testWindow  Brackets popup window
@param {string} extraFilePath  Absolute path for the extra result file