StringAssertions - Count regex matches

[ITaluone]

Description

I am using the FA string assertions MatchRegex() to check strings. But because the regex pattern have to be really generic to match all future strings, it turned out to be a test case that will mostly ever pass (and therefore is useless).

Now if I could restrict the assertion to a predictable count of regex matches, this could be (for me) a better solution.

Complete minimal example reproducing the issue

class A
{
    public string LongLongString = "Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est (100,00€)Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore (104,23€)magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.";
}

[Fact]
public void Test_Regex_matches()
{
    // Arrange
    var a = new A();
    
    // Act / Assert
    // Matching e.g. "(100,00€)"
    a.LongLongString.Should().MatchRegex(@"(.*\(\d+,\d{2}€\))+", Exactly.Twice());
}

Expected behavior:

I think an overload like the string.Contains("bla", AtLeast.Once()) should be good, so:
a.LongLongString().Should().MatchRegex("bla", Exactly.Twice());

Actual behavior:

Cannot be done (except I am missing some way to achieve this)

Versions

• Which version of Fluent Assertions are you using? -> 6.4.0
• Which .NET runtime and version are you targeting? .NET Core 3.1

Additional Information

Unfortunately string.Contains("bla", AtLeast.Once()) and similar assertions can not be done, because I am trying to match price values inside the text.

[jnyrup]

You can achieve it using the Match() assertion, but it's not pretty and the failure message will be poor.

a.LongLongString.Should().Match(subject => Regex.Matches(subject, @"(.*\(\d+,\d{2}€\))+").Count == 2);

[ITaluone]

Ok, thank you

I will take that for the moment to be able to go further in development. Helps a lot :)

[IT-VBFK]

If you have a small hint for me how to start I would give it a shot

[jnyrup]

@IT-VBFK Have a look at how the Contain overload that takes an OccurrenceConstraint works.
To calculate the number of occurrences to pass to ForConstraint use Regex.Matches().Count instead of CountSubstring.

[IT-VBFK]

Ok will try to implement this :)

Should this be an extra overload for both of the MatchRegex() methods?

[jnyrup]

Should this be an extra overload for both of the MatchRegex() methods?

Yes please.

[jnyrup]

If it's of any help Contain(string, OccurrenceConstraint) was added in #1145