Add have_key matcher

src/spectator/dsl/matcher_dsl.cr

@@ -395,6 +395,23 @@ module Spectator::DSL
       ::Spectator::Matchers::HaveMatcher.new({{expected.splat.stringify}}, {{expected}})
     end
 
+    # Indicates that some set, such as a `Hash`, has a given key.
+    # The `has_key?` method is used for this check.
+    #
+    # Examples:
+    # ```
+    # expect({foo: "bar"}).to have_key(:foo)
+    # expect({"lucky" => 7}).to have_key("lucky")
+    # ```
+    macro have_key(expected)
+      ::Spectator::Matchers::HasKeyMatcher.new({{expected.stringify}}, {{expected}})
+    end
+
+    # ditto
+    macro has_key(expected)
+      have_key({{expected}})
+    end
+
     # Indicates that some value should have a set of attributes matching some conditions.
     # A list of named arguments are expected.
     # The names correspond to the attributes in the instance to check.

src/spectator/matchers/have_key_matcher.cr

@@ -0,0 +1,25 @@
+require "./value_matcher"
+
+module Spectator::Matchers
+  # Matcher that tests whether a `Hash` (or similar type) has a given key.
+  # The set is checked with the `has_key?` method.
+  struct HaveKeyMatcher(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)
+      partial.actual.has_key?(expected)
+    end
+
+    # Describes the condition that satisfies the matcher.
+    # This is informational and displayed to the end-user.
+    def message(partial)
+      "Expected #{partial.label} to have key #{label}"
+    end
+
+    # Describes the condition that won't satsify the matcher.
+    # This is informational and displayed to the end-user.
+    def negated_message(partial)
+      "Expected #{partial.label} to not have key #{label}"
+    end
+  end
+end