Dart unittest produces unhelpful output

Question

I am working through the AngularDart tutorial and trying to write unit tests as I complete the exercises.

I have a test that looks like this:

test('should convert sugar ingredient to maple syrup', inject((SugarFilter filter) {
  var r1 = new Recipe(null, null, null, ['has sugar in ingredients '], 'bla', null, null);
  var r1New = new Recipe(null, null, null, ['has maple syrup in ingredient '], 'bla', null, null);
  var r2 = new Recipe(null, null, null,[ 'has pure ingredients'], 'bla', null, null);
  var inList = [r1, r2];
  var outList = [r1New, r2];
  expect(filter(inList), equals(outList));
}));

The test fails with this output:

Test failed: Caught Expected: [Instance of 'Recipe', Instance of 'Recipe']
  Actual: [Instance of 'Recipe', Instance of 'Recipe']
   Which: was <Instance of 'Recipe'> instead of <Instance of 'Recipe'> at location [0]

I tried modifying the existing test for 'categoryFilter' to make that fail and I get the same, rather unhelpful output.

Is there a way to make the output from the comparison of two objects more meaningful?

Answer 1

What exactly do you expect when you compare two lists which contain different objects? Should they be equal because each list contains two Receipe instances? What is filter() anyway?

Two lists are only equal if it is the same list:

expect(inList, equals(inList));

You can use a matcher like everyElement, orderedEquals or unorderedEquals to compare the contents of a list. But if you put different instances into the list even if they are of the same class the comparsion will still fail.

If you want the comparsion to behave differently you have to override the equals() method of the Receipe class (this requires also to override get hashCode).

You could override the toString() method in Receipe to get a better error message, for example adding the value of some fields to the output string.

@override
String toString() => '${super.toString()} ${name}'; // I don't know if the Receipe class has a name field though