Move value enumeration to another type

src/spectator/formatting/failure_block.cr

@@ -62,8 +62,8 @@ module Spectator::Formatting
       io.puts
       indent do
         @result.expectations.each_unsatisfied do |expectation|
-          expectation.values.each do |key, value|
-            line(io, MatchDataValuePair.new(key, value))
+          MatchDataValues.new(expectation.values).each do |pair|
+            line(io, Color.failure(pair))
           end
         end
       end

src/spectator/formatting/match_data_values.cr

@@ -0,0 +1,18 @@
+module Spectator::Formatting
+  # Produces a `MatchDataValuePair` for each key-value pair
+  # from `Spectator::Matchers::MatchData#values`.
+  private struct MatchDataValues(T)
+    include Enumerable(MatchDataValuePair)
+
+    # Creates the values mapper.
+    def initialize(@values : T)
+    end
+
+    # Yields pairs that can be printed to output.
+    def each
+      @values.each do |key, value|
+        yield MatchDataValuePair.new(key, value)
+      end
+    end
+  end
+end