public void BeginFactor_WhenGivenAToken_PushesFactorNode() { // Arrange: var token = new Token { TokenKind = TokenKind.String, Image = "<F>" }; var stack = new Stack <IAstNode>(); stack.Push(_nodeFactoryMock.Object.Create(AstNodeType.Term, token)); var builder = new AstBuilder(_nodeFactoryMock.Object, null, stack, _tracerMock.Object); // Act: builder.BeginFactor(token); // Assert: Assert.That(stack.Count, Is.EqualTo(2)); Assert.That(stack.Peek(), Is.InstanceOf(typeof(IFactorNode))); Assert.That((stack.Peek() as IFactorNode)?.Image, Is.EqualTo(token.Image)); }