Invoking should support Func<TInput, TResult>

Description

Properties are merely functions in disguise, and it would be useful to be able to assert on exceptions that they might throw, for example that accessing a property of a disposed object throws an ObjectDisposedException.

This doesn’t work today because a simple lambda that accesses a property is compiled as a Func<TInput, TResult>, but there is no corresponding overload that can accept this delegate type.

Complete minimal example reproducing the issue

class MyDisposable : IDisposable
{
  // the usual Disposable implementation elided here

  bool IsConnected
  {
    get
    {
      if (disposed) throw new ObjectDisposedException(GetType().Name);
      return _isConnected;
    }
  }
}

// Arrange
var subject = new MyDisposable();

// Act
subject.Dispose();

// Assert
subject.Invoking(it => it.IsConnected).Should().Throw<ObjectDisposedException>();

Expected behavior:

I would expect this to invoke the lambda, and verify that the specified exception was thrown.

Actual behavior:

Compilation failure.

Versions

Using FluentAssertions 5.4.1, running on .NET Core 2.0

[dennisdoomen]

Alright, it seems that Invoking is the best option considering the various situations we need to cover.

[jnyrup]

As I understand the notation of Get it is mainly intended for getters, such as properties that only returns the value of the underlying backing field or methods that does very little computation. For other scenarios, e.g. IO operations, Find or Load might be more proper prefixes.

Func<T, TResult> can match a property, where Getting would be a fine name, but it also matches many other cases, where the semantics mismatches.

That’s why I dislike Getting since it imposes semantics we know nothing about.