Mocking with Dart


I’ve been trying to get my head around the mocking library in dart, but it seems I’ve still not got it.

In my library, I have an HTTP request to an external resource, which I would like to mock as to not rely on the external resource all the time.

The main class in my library looks like this:

SampleClass(String arg1, String arg2, [http.Client httpClient = null]) {
    this._arg1 = arg1;
    this._arg2 = arg2;
    _httpClient = (httpClient == null) ? http.Request : httpClient;

So I have prepared my class to receive http.client as an argument, as this is what I would like to mock.

So in my unit tests file I’ve created:

class HttpClientMock extends Mock implements http.Client {
  noSuchMethod(i) => super.noSuchMethod(i);

And on my unit test I have done:

var mockHttpClient = new HttpClientMock()
        ..when(callsTo('send')).alwaysReturn("this is a test");

I would then expect that every time I called “send” from my library, which has been instanciated in my unit tests with the optional “httpClient”, that it would return “this is a test”. I’m pretty sure I’m missing somethign very big here, but can’t quite put my finger on what.

Any help appreciated.


I’m not sure what you are missing because your example works for me:

void main() {
  test('bla', () {
    var mockHttpClient = new HttpClientMock()
            ..when(callsTo('send')).alwaysReturn("this is a test");

    http.Request req = new http.Request('POST', Uri.parse(''));
    var s = mockHttpClient.send(req);
    expect(mockHttpClient.send(req), equals('this is a test'));


Answered By – Günter Zöchbauer

Answer Checked By – Katrina (FlutterFixes Volunteer)

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