How to express an expected call on a Moq mock in the memberdata for an XUnit Theory.

In XUnit you can use the [Theory] attribute to run the same test against a set of different parameters. Moq allows you to specify expectations on which methods of a mocked interface are called, with the Verify method. Recently, I wanted to combine these two techniques to be able to convey the expectation along with the other test parameters to the XUnit Theory. It took me a little thought to get this right. The trick is in casting the expected call (usually an Action<T>) to an Expression<Action<T>>. That is done in the gist below.

	using System;
	using System.Collections.Generic;
	using System.Linq.Expressions;
	using Moq;
	using Xunit;
	namespace DynamicVerify
	{
	public class ExpectedCallFromMemberData
	{
	[Theory]
	[MemberData(nameof(GetMemberData))]
	public void Bar_calls_right_method_on_IFoo(int number, Expression<Action<IFoo>> expectedCall, Times times, string message)
	{
	var fooMock = new Mock<IFoo>();
	var sut = new Bar(fooMock.Object);
	sut.DoBar(number);
	fooMock.Verify(expectedCall, times, message);
	}
	private static IEnumerable<object[]> GetMemberData()
	{
	Func<Expression<Action<IFoo>>, Expression<Action<IFoo>>> fooCall = action => action;
	return new List<object[]> {
	new object[] {1, fooCall(foo => foo.DoFoo1()), Times.Once(), "Expected call on DoFoo1." },
	new object[] {2, fooCall(foo => foo.DoFoo2()), Times.Once(), "Expected call on DoFoo2." },
	new object[] {3, fooCall(foo => foo.DoFoo1()), Times.Never(), "Argument 3 should not call IFoo at all." },
	};
	}
	}
	public interface IFoo
	{
	void DoFoo1();
	void DoFoo2();
	}
	public class Bar
	{
	private IFoo _foo;
	public Bar(IFoo foo)
	{
	_foo = foo;
	}
	public void DoBar(int number)
	{
	if (number == 1)
	_foo.DoFoo1();
	else if (number == 2)
	_foo.DoFoo2();
	}
	}
	}

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