componentDidMount Jest中的测试承诺错误

Question

我在测试componentDidMount()内的承诺失败时会发生什么问题。以下是相关代码：

//TEST FILE
it('should show an error message when ZipkinService is down', async () => {
    const getTraces = ZipkinService.getTraces.mockImplementation(() => Promise.reject('FAIL'));
    const getTraceById = ZipkinService.getTraceById.mockImplementation(() => Promise.reject('FAIL'));
    const tree = Enzyme.mount(
        <TraceListComponent value={''} />
    );
    await tree.instance().componentDidMount();
    console.log(tree.debug());
    expect(tree.state().error).toBe('FAIL');
});

//REACT COMPONENT
componentDidMount() {
    return this.refreshData(this.props.value);
}

public refreshData(value: string) {
    let self = this;
    if (value !== '') {
        return ZipkinService.getTraceById(value).then(function(trace) {
            self.setState({traceList: [trace], error: undefined});
        }).catch(function(errorMessage) {
            self.setState({traceList: [], error: errorMessage});
        });
    }
    else {
        return ZipkinService.getTraces().then(function(traces) {
            self.setState({traceList: traces, error: undefined});
        }).catch(function(errorMessage) {
            console.log("CATCH HERE");
            self.setState({traceList: [], error: errorMessage});
        });
    }
}

但是测试总是失败并不重要，我无法弄清楚原因。我能得到的最接近的是把期望置于process.nextTick()之内，但这似乎是错误的。我注意到基于打印语句，它是因为测试发生在之前实际更新错误。因此，每次测试运行时，它都会在更新之前获得undefined。