testMockMethod() {
    const mockRange = new MockRange();
    mockRange.getStartOffset().$returns(42);
    mockRange.$replay();

    assertEquals(
        'Mock method should return recorded value', 42,
        mockRange.getStartOffset());
    mockRange.$verify();
  }
Tests that a MockRange can be created successfully, a call to a mock
method can be recorded, and the correct behavior replayed and verified.
@suppress {missingProperties} suppression added to enable type checking