Static factories for creating Matchers using lambdas #440

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1. rmcdouga commented on Aug 24, 2025

   

   rmcdouga

   on Aug 24, 2025

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   I have a PR ready to create that has two static factories - one for TypeSafeDiagnosingMatcher and one for FeatureMatcher. I haven't created a static factory in all classes as I believe that these two are the primary ones used for creating custom Matcher implementations. If there are other classes that are commonly used for custom matchers, let me know and I can look into creating static factories for those as well.

   The static factory method signature for TypeSafeDiagnosingMatcher looks like this:

   public static <T> Matcher<T> matcher(Predicate<T> predicate, final String successDescription, final String failureDescription, Class<T> expectedType)

   A sample matcher looks like this:

   /**
    * A matcher that checks if a directory exists.
    * @return the file matcher
    */
   public static Matcher<Path> anExistingDirectory() {
       return matcher(Files::isDirectory, "an existing directory", "is not a directory", Path.class);
   }

   The static factory method signature for FeatureMatcher looks like this:

   public static <T,F> Matcher<T> matcher(final Matcher<F> expected, final Function<T, F> extractor, String featureDescription, String featureName, Class<T> expectedType)

   A sample FeatureMatcher matcher looks like this:

   /**
     * A matcher that checks if a file size matches an expected size.
     * @param expected matcher for the expected size
     * @return the file matcher
     */
   public static Matcher<Path> hasSize(final Matcher<Long> expected) {
       return FeatureMatcher.matcher(expected, p->toUncheckedEx(()->Files.size(p)), "A file with size", "size", Path.class);
   }

   instead of

    /**
      * A matcher that checks if a file size matches an expected size.
      * @param expected matcher for the expected size
      * @return the file matcher
      */
    public static Matcher<Path> hasSize(final Matcher<Long> expected) {
        return new FeatureMatcher<Path, Long>(expected, "A file with size", "size") {
               @Override protected Long featureValueOf(Path actual) { return toUncheckedEx(()->Files.size(actual)); }
       };
   }