Evaluating Multiple Test Assertions At Once With FluentAssertions

When typically writing unit tests you would typically follow the AAA pattern - arrange, act, assert. This basically means you set up the test, execute your logic, and then have at least one assertion to verify your expected behaviour.

Let us take, for example, the following class:

public static class Squares
{
    public static int Square(int n) => n * n;
}

Let us write tests for this class:

public class SquareTests
{
    [Theory]
    [InlineData(-3, -10)]
    [InlineData(3, -10)]
    public void Square_Computes_Correctly(int number, int square)
    {
        var result = Squares.Square(number);
        result.Should().BeNegative();
        result.Should().Be(square);
    }
}

The test data is wrong to demonstrate a point.

If we run these tests, they will fail with the following error:

What is happening here is that the first assertion, result.Should().BePositive() fails, and the test runner stops immediately and moves on to the next test.

Sometimes, you want to evaluate all the assertions at once so that you can know well in advance how badly off you are around your logic. It can be tedious to fix one error, run and then find you have yet another error. In this scenario, you would want to know all the failed assertions so that you can fix the logic once and for all.

This can be resolved using an AssertionScope.

We can rewrite our code as follows to add an AssertionScope.

[Theory]
[InlineData(-3, -10)]
[InlineData(3, -10)]
public void Square_Computes_Correctly(int number, int square)
{
    var result = Squares.Square(number);
    using (new AssertionScope())
    {
        result.Should().BeNegative();
        result.Should().Be(square);
    }
}

If we run the tests, the following will be the results:

Here we can see, both assertions were evaluated, and the results were output to the console.

TLDR

FluentAssertions has the AssertionScope that allows you to evaluate multiple assertions at once.

Happy hacking!