Add basic range matcher

src/spectator/matchers/range_matcher.cr

@@ -0,0 +1,27 @@
+require "./value_matcher"
+
+module Spectator::Matchers
+  # Matcher that tests whether a value is in a given range or set of values.
+  # The `#includes?` method is used for this check.
+  # Typically this matcher uses a `Range`,
+  # but any type that implements the `#includes?` method is supported.
+  struct RangeMatcher(ExpectedType) < ValueMatcher(ExpectedType)
+    # Determines whether the matcher is satisfied with the value given to it.
+    # True is returned if the match was successful, false otherwise.
+    def match?(partial : Expectations::ValueExpectationPartial(ActualType)) : Bool forall ActualType
+      @expected.includes?(partial.actual)
+    end
+
+    # Describes the condition that satisfies the matcher.
+    # This is informational and displayed to the end-user.
+    def message(partial : Expectations::ValueExpectationPartial(ActualType)) : String forall ActualType
+      "Expected #{partial.label} to be in #{label}"
+    end
+
+    # Describes the condition that won't satsify the matcher.
+    # This is informational and displayed to the end-user.
+    def negated_message(partial : Expectations::ValueExpectationPartial(ActualType)) : String forall ActualType
+      "Expected #{partial.label} to not be in #{label}"
+    end
+  end
+end