How to use the gemini-core.promiseUtils.waitForResults function in gemini-core

_runTests(suiteCollection) {
        this.emit(Events.BEGIN_SESSION);

        return _(this._getBrowsersToRun())
            .map((browserId) => this._runTestsInBrowser(suiteCollection, browserId))
            .thru(promiseUtils.waitForResults)
            .value()
            .finally(() => this.emit(Events.END_SESSION));
    }

run(suiteCollection, stateProcessor) {
        const suites = suiteCollection.clone().allSuites();

        return _(suites)
            .filter((suite) => _.includes(suite.browsers, this._browserId))
            .map((suite) => {
                if (suite.hasOwnProperty('url')) {
                    Object.defineProperty(suite, 'fullUrl', {
                        get: () => this._mkFullUrl(suite.url)
                    });
                }

                return this._runSuite(suite, stateProcessor);
            })
            .thru(promiseUtils.waitForResults)
            .value();
    }

run(suiteCollection, stateProcessor) {
        const suites = suiteCollection.clone().allSuites();

        return _(suites)
            .filter((suite) => _.includes(suite.browsers, this._browserId))
            .map((suite) => {
                if (suite.hasOwnProperty('url')) {
                    Object.defineProperty(suite, 'fullUrl', {
                        enumerable: true,
                        get: () => this._mkFullUrl(suite.url)
                    });
                }

                return this._runSuite(suite, stateProcessor);
            })
            .thru(promiseUtils.waitForResults)
            .value();
    }