Add instance_of matcher to check exact type

src/spectator/dsl/matchers.cr

@@ -122,6 +122,32 @@ module Spectator
       be_a({{expected}})
     end
 
+    # Indicates that some value should be of a specified type.
+    # The value's runtime class is checked.
+    # A type name or type union should be used for *expected*.
+    #
+    # Examples:
+    # ```
+    # expect(123).to be_instance_of(Int32)
+    # ```
+    macro be_instance_of(expected)
+      ::Spectator::Matchers::InstanceMatcher({{expected}}).new
+    end
+
+    # Indicates that some value should be of a specified type.
+    # The value's runtime class is checked.
+    # A type name or type union should be used for *expected*.
+    # This method is identical to `#be_an_instance_of`,
+    # and exists just to improve grammar.
+    #
+    # Examples:
+    # ```
+    # expect(123).to be_an_instance_of(Int32)
+    # ```
+    macro be_an_instance_of(expected)
+      be_instance_of({{expected}})
+    end
+
     # Indicates that some value should respond to a method call.
     # One or more method names can be provided.
     #

src/spectator/matchers/instance_matcher.cr

@@ -0,0 +1,57 @@
+require "./matcher"
+
+module Spectator::Matchers
+  # Matcher that tests a value is of a specified type.
+  struct InstanceMatcher(Expected) < StandardMatcher
+    # Short text about the matcher's purpose.
+    # This explains what condition satisfies the matcher.
+    # The description is used when the one-liner syntax is used.
+    def description : String
+      "is an instance of #{Expected}"
+    end
+
+    # Checks whether the matcher is satisifed with the expression given to it.
+    private def match?(actual : TestExpression(T)) : Bool forall T
+      actual.value.class == Expected
+    end
+
+    # Message displayed when the matcher isn't satisifed.
+    #
+    # This is only called when `#match?` returns false.
+    #
+    # The message should typically only contain the test expression labels.
+    # Actual values should be returned by `#values`.
+    private def failure_message(actual) : String
+      "#{actual.label} is not an instance of #{Expected}"
+    end
+
+    # Message displayed when the matcher isn't satisifed and is negated.
+    # This is essentially what would satisfy the matcher if it wasn't negated.
+    #
+    # This is only called when `#does_not_match?` returns false.
+    #
+    # The message should typically only contain the test expression labels.
+    # Actual values should be returned by `#values`.
+    private def failure_message_when_negated(actual) : String
+      "#{actual.label} is an instance of #{Expected}"
+    end
+
+    # Additional information about the match failure.
+    # The return value is a NamedTuple with Strings for each value.
+    private def values(actual)
+      {
+        expected: Expected.to_s,
+        actual:   actual.value.class.inspect,
+      }
+    end
+
+    # Additional information about the match failure when negated.
+    # The return value is a NamedTuple with Strings for each value.
+    private def negated_values(actual)
+      {
+        expected: "Not #{Expected}",
+        actual:   actual.value.class.inspect,
+      }
+    end
+  end
+end