public AndConstraint<TAssertions> MatchRegex( 
   string regularExpression,
   OccurrenceConstraint occurrenceConstraint,
   string because,
   params object[] becauseArgs
)

Parameters

regularExpression

The regular expression with which the subject is matched.

occurrenceConstraint

A constraint specifying the expected amount of times a regex should match a string. It can be created by invoking static methods Once, Twice, Thrice, or Times(int) on the classes FluentAssertions.Exactly, FluentAssertions.AtLeast, FluentAssertions.MoreThan, FluentAssertions.AtMost, and FluentAssertions.LessThan. For example, FluentAssertions.Exactly.Times or FluentAssertions.LessThan.Twice.

because

A formatted phrase as is supported by System.String.Format(System.String,System.Object[]) explaining why the assertion is needed. If the phrase does not start with the word because, it is prepended automatically.

becauseArgs

Zero or more objects to format using the placeholders in because.

Reference

StringAssertions<TAssertions> Class
StringAssertions<TAssertions> Members
Overload List
Exactly Class
AtLeast Class
MoreThan Class
AtMost Class
LessThan Class
Times Method
Twice Method
System.String.Format(System.String,System.Object[])