toContain method
Returns a matcher that matches if the match argument contains the expected value.
For Strings this means substring matching;
for Maps it means the map has the key, and for Iterables it means
the iterable has a matching element.
In the case of iterables, expected
can itself be a matcher.
expect('Hello world').toContain('Hello');
expect([1,2]).toContain(2);
expect({ 'hello': 'world' }).toContain('hello');
Implementation
Return toContain(Object? expected) {
return runMatcher(dart_test.contains(expected));
}