How to use Fluent Assertions to test for exception in inequality tests?

Question

I'm trying to write a unit test for a greater than overridden operator using Fluent Assertions in C#. The greater than operator in this class is supposed to throw an exception if either of the objects are null.

Usually when using Fluent Assertions, I would use a lambda expression to put the method into an action. I would then run the action and use action.ShouldThrow<Exception>. However, I can't figure out how to put an operator into a lambda expression.

I would rather not use NUnit's Assert.Throws(), the Throws Constraint, or the [ExpectedException] attribute for consistencies sake.

Answer 1

You may try this approach.

[Test] public void GreaterThan_NullAsRhs_ThrowsException() {     var lhs = new ClassWithOverriddenOperator();     var rhs = (ClassWithOverriddenOperator) null;      Action comparison = () => { var res = lhs > rhs; };      comparison.Should().Throw<Exception>(); } 

It doesn't look neat enough. But it works.

Or in two lines

Func<bool> compare = () => lhs > rhs; Action act = () => compare();