FluentAssertion, check constraint just for condition-CodePudding

Inside a c# test I'm asserting with FluentAssertion. But, in this test, the "assert" only should be executed under a condition (when result is not valid)

This is my actual code:

if (!result.IsValid)
{
    result
        .Errors
        .Should()
        .Contain(e => e.ErrorMessage == MYERROR);
}

In my opinion, this code looks ugly, and I would like to rewrite in a more elegant way, something like this:

// -- DON'T COPY PASTE THIS CODE, IT DON'T COMPILE -- //
result
    .Errors
    .Should()
    .When(!result.IsValid) //<-- something like this
    .Contain(e => e.ErrorMessage == MYERROR);
// -- DON'T COPY PASTE THIS CODE, IT DON'T COMPILE -- //

Notice, in my sample, result is a FluentValidation's ValidationResult

What would be the right syntax for this code. Maybe, this is an XY problem, and I'm focused on the wrong side of the issue.

The full test:

[Theory]
[InlineData("hola", true, "Its ok", null)]
[InlineData("hola\tadeu", false, "Not ok, contains a tab (no printable char)", MYERROR)]
public void OnlyPrintableCharsTest(string name, bool expected, string because, string? errorMsg)
{
    // -- ARRANGE --
    var persona =
        new
        Persona() { Name = nom };

    // -- ACT --

    var result =
        MyCustomOnlyPrintableCharsValidator
        .Validate(persona);

    // -- ASSERT --
    result
        .IsValid
        .Should()
        .Be(expected, because);

    if (!result.IsValid) // <-- Ugly code
    {
        result
            .Errors
            .Should()
            .Contain(e => e.ErrorMessage == errMsg);
    }
}

CodePudding user response：

You can choose to have a separate test for the positive (true) and negative (false) scenario.

From a unit testing best practices document from Microsoft:

If logic in your test seems unavoidable, consider splitting the test up into two or more different tests.

That also simplifies the InlineData setup; the null for errorMsg in the positive scenario can be discarded.
Maybe you can switch to [Fact] tests?