Update EmptyMatcher to use MatchData

spec/matchers/empty_matcher_spec.cr

@@ -1,13 +1,16 @@
 require "../spec_helper"
 
 describe Spectator::Matchers::EmptyMatcher do
-  describe "#match?" do
+  describe "#match" do
+    context "returned MatchData" do
+      describe "#matched?" do
         context "with an empty set" do
           it "is true" do
             array = [] of Symbol
             partial = new_partial(array)
             matcher = Spectator::Matchers::EmptyMatcher.new
-        matcher.match?(partial).should be_true
+            match_data = matcher.match(partial)
+            match_data.matched?.should be_true
           end
         end
 
@@ -16,7 +19,30 @@ describe Spectator::Matchers::EmptyMatcher do
             array = %i[a b c]
             partial = new_partial(array)
             matcher = Spectator::Matchers::EmptyMatcher.new
-        matcher.match?(partial).should be_false
+            match_data = matcher.match(partial)
+            match_data.matched?.should be_false
+          end
+        end
+      end
+
+      describe "#values" do
+        context "expected" do
+          it "is an empty set" do
+            array = %i[a b c]
+            partial = new_partial(array)
+            matcher = Spectator::Matchers::EmptyMatcher.new
+            match_data = matcher.match(partial)
+            match_data.values[:expected].size.should eq(0)
+          end
+        end
+
+        context "actual" do
+          it "is the actual set" do
+            array = %i[a b c]
+            partial = new_partial(array)
+            matcher = Spectator::Matchers::EmptyMatcher.new
+            match_data = matcher.match(partial)
+            match_data.values[:actual].should eq(array)
           end
         end
       end
@@ -27,7 +53,8 @@ describe Spectator::Matchers::EmptyMatcher do
           label = "everything"
           partial = new_partial(array, label)
           matcher = Spectator::Matchers::EmptyMatcher.new
-      matcher.message(partial).should contain(label)
+          match_data = matcher.match(partial)
+          match_data.message.should contain(label)
         end
       end
 
@@ -37,7 +64,10 @@ describe Spectator::Matchers::EmptyMatcher do
           label = "everything"
           partial = new_partial(array, label)
           matcher = Spectator::Matchers::EmptyMatcher.new
-      matcher.negated_message(partial).should contain(label)
+          match_data = matcher.match(partial)
+          match_data.negated_message.should contain(label)
+        end
+      end
     end
   end
 end

src/spectator/matchers/empty_matcher.cr

@@ -11,26 +11,38 @@ module Spectator::Matchers
 
     # Determines whether the matcher is satisfied with the partial given to it.
     # `MatchData` is returned that contains information about the match.
-    def match(partial) : MatchData
-      raise NotImplementedError.new("#match")
+    def match(partial)
+      actual = partial.actual
+      matched = actual.empty?
+      MatchData.new(matched, actual, partial.label)
     end
 
-    # 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.empty?
+    # Match data specific to this matcher.
+    private struct MatchData(T) < MatchData
+      # Creates the match data.
+      def initialize(matched, @actual : T, @actual_label : String)
+        super(matched)
+      end
+
+      # Information about the match.
+      def values
+        {
+          expected: [] of Nil,
+          actual:   @actual,
+        }
       end
 
       # Describes the condition that satisfies the matcher.
       # This is informational and displayed to the end-user.
-    def message(partial)
-      "Expected #{partial.label} to be empty"
+      def message
+        "#{@actual_label} is empty"
       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 be empty"
+      def negated_message
+        "#{@actual_label} is not empty"
+      end
     end
   end
 end