FluentAssertion fail to compare enumerable of strings

Question

This code works fine

    [Test]
    public void boo()
    {
        var collection = new[] { 1, 2, 3 };
        collection.Should().Equal(1, 2, 3);
    }

But, this fails

    [Test]
    public void foo()
    {
        var collection = new[] { "1", "2", "3" };
        collection.Should().Equal("1", "2", "3");            
    }

The failure message is:

'Expected collection to be equal to {1} because 2, but {"1", "2", "3"} contains 2 item(s) too many.'

What is wrong here? Why enumerable of string could not be compared?

And, of cause, my question is - how to handle case in foo() ?

Answer 1

This happens because the compiler selects the wrong overload of Equals() because of limitations in C#. In your particular case, it's taking the Equals(string expected, string reason, params string[] args), instead of Equals(IEnumerable). I have never found an easy way to solve this ambiguity in FluentAssertions.

To solve your problem, wrap the expected values in an array.

[Test] 
public void foo()  
{ 
  var collection = new[] { "1", "2", "3" }; 
  collection.Should().Equal(new[] {"1", "2", "3"});              
}

Answer 2

The problem is that the 2nd call is resolved to the following overload:

public AndConstraint<TAssertions> Equal(IEnumerable expected, 
                                        string reason, 
                                        params object[] reasonArgs); 

Instead of:

public AndConstraint<TAssertions> Equal(params object[] elements);

To get the desired result you can force the compiler to the right overload method, for example by doing:

collection.Should().Equal((object)"1", "2", "3");

Answer 3

What happens with the test of:

[Test]
public void foo()
{
    const string one = "1";
    const string two = "2";
    const string three = "3";
    var collection = new[] { one, two, three };
    collection.Should().Equal(one, two, three);            
}

I assume as Kenny acknowledged in a comment that you're doing reference equality where those strings are not the same reference.

Answer 4

Try SequenceEquals instead?

http://msdn.microsoft.com/en-us/library/bb342073.aspx

And the Equals method is just comparing the references for equality.

Here's a line from a unit test in one of my projects:

Assert.IsTrue(expected.OrderBy(x => x).SequenceEqual(actual.OrderBy(x => x)));

All of the elements in "expected" and "actual" implement IEQuatable.