Assertions in Dart and Flutter tests: matcher operators

This is the part of the ultimate cheat sheet dedicated to:

• matcher operators.

In this series:

• expect and matcher
• equality matchers
• type and error matchers
• collection matchers
• numeric and comparable matchers
• universal and custom matchers
• matcher operators
• asynchronous expect and matchers
• Flutter widget matchers
• accessibility matchers
• golden matchers
• mock invocations and parameters

Matcher operators

allOf

The allOf matcher allows combining multiple matchers and ensures all of them are satisfied. It can be used with an array of matchers or with up to 7 individual matchers:

test('expect: allOf ✅', () {
  final result = Result(0);
  expect(result, allOf(hasValue(0), isResult));
  expect(result, allOf([hasValue(0), isResult]));
});

In case of failure:

test('expect: allOf ❌', () {
  final result = Result(0);
  expect(result, allOf([hasLength(1), hasValue(1)]));
});

The output prints errors from the first failed matcher:

Expected: (an object with length of <1> and an object with value property of <1>)
  Actual: Result:<Result{result: 0}>
   Which: has no length property

anyOf

The anyOf matcher also accepts an array of matchers or up to 7 individual matchers and ensures at least one of them is satisfied:

test('expect: anyOf ✅', () {
  final result = Result(0);
  expect(result, anyOf(hasLength(1), hasValue(0)));
  expect(result, anyOf([hasLength(1), hasValue(0)]));
});

Even though hasLength matcher fails, the overall test passes.

isNot

The isNot matcher calls the inner matcher and inverts its matching result:

test('expect: isNot ✅', () {
  final result = 0;
  expect(result, isNot(1));
  expect(result, isNot(isResult));
  expect(result, isNot(allOf(isResult, hasValue(0))));
});

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