Redesign MockConvas

[st-pasha]

Currently MockCanvas serializes all method calls into strings and stores them all in an internal list. That list is later tested to see if it contains "correct" strings. Something like this:

      final calls = canvas.methodCalls;
      expect(calls.length, 6);
      expect(
        calls[0],
        'transform(1.0, 0.0, 0.0, 0.0, -0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 23.0, 17.0, 0.0, 1.0)',
      );
      expect(calls[1], 'drawRect(0.0, 0.0, 10.0, 10.0)');
      expect(calls[2], 'drawLine(0.0, -2.0, 0.0, 2.0)');
      expect(calls[3], 'drawLine(-2.0, 0.0, 2.0, 0.0)');
      expect(calls[4], 'drawParagraph(?, -30.0, -15.0)');
      expect(calls[5], 'drawParagraph(?, -20.0, 10.0)');

This has several disadvantages, the chief among which is numeric instability. For example, the string "0.0" is different from "-0.0", though both represent exactly the same numeric quantity. In general, the only way to write a more-or-less reliable test then is to make sure to always use very round numbers (like in the example above), and even that does not always work perfectly.

Suggestion

I suggest then changing the internal structure of MockCanvas so that instead of storing strings it would store individual drawing commands, and provide the == operator which would compare canvases up to certain numeric precision. So, the usage code could become something like this:

final canvas = MockCanvas();
// draw something on canvas here
// ...
// now test that the correct drawing commands were issued:
expect(
  canvas,
  MockCanvas()
    ..translate(23, 17)
    ..drawRect(0, 0, 10, 10)
    ..drawLine(0, -2, 0, 2)
    ..drawLine(-2, 0, 2, 0)
    ..drawParagraph(-30, -15)
    ..drawParagraph(-20, 10),
);

[spydon]

Sounds great, it will be much easier to read what is happening too.

[luanpotter]

I love it! One caveat is to have a nice to way to do some sort of "contains actions" if you don't wanna check the whole sequence of actions on some tests.

[erickzanardo]

Sounds very good!

[spydon]

Do you want to take on this task @st-pasha? :)

[st-pasha]

sure, just convert this discussion into an issue and assign