Meziantou.Framework

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Substrings, prefixes and suffixes

The substring, prefix or suffix you look for comes first, then the text under test:

var message = "Hello, World!";

Assert.Contains("World", message);                        // ordinal comparison by default
Assert.Contains("world", message, ignoreCase: true);      // OrdinalIgnoreCase
Assert.Contains("WORLD", message, StringComparison.OrdinalIgnoreCase);
Assert.DoesNotContain("Goodbye", message);

Assert.StartsWith("Hello", message);
Assert.EndsWith('!', message);
Assert.DoesNotStartWith("World", message);
Assert.DoesNotEndWith("?", message);
  • Contains, DoesNotContain, StartsWith, EndsWith, DoesNotStartWith and DoesNotEndWith accept a string, a char or a ReadOnlySpan<char>.
  • The comparison is ordinal by default. Pass ignoreCase: true for StringComparison.OrdinalIgnoreCase, or a StringComparison for any other comparison, such as StringComparison.CurrentCulture.
  • A message passed as the third argument, Assert.DoesNotContain("secret", log, "the log must not leak it"), is the message of the assertion: the two strings are still compared as text.
  • A null text fails the assertion instead of being treated as an empty string.
  • When DoesNotContain fails, the message shows the index where the text was found.

To compare a whole string, use Assert.Equal, which can also ignore the case and the line endings. See Equality.

Regular expressions

var version = "v2.10.3";

Assert.Matches(@"^v\d+\.\d+\.\d+$", version);   // the pattern comes first
Assert.DoesNotMatch("-preview", version);

Matches and DoesNotMatch take a pattern or a Regex. A pattern is evaluated with the default match timeout, like Regex.IsMatch(input, pattern). Pass a Regex to choose options or a timeout, or to reuse a generated regular expression.