Create a type to output a key-value pair

src/spectator/formatters/failure_block.cr

@@ -63,11 +63,7 @@ module Spectator::Formatters
       indent do
         @result.expectations.each_unsatisfied do |expectation|
           expectation.values.each do |key, value|
-            line(io) do
+            line(io) { io << MatchDataValuePair.new(key, value) }
-              io << key
-              io << ": "
-              io << value
-            end
           end
         end
       end

src/spectator/formatters/match_data_value_pair.cr

@@ -0,0 +1,15 @@
+module Spectator::Formatters
+  # A single key-value pair from the `Spectator::Matchers::MatchData#value` method.
+  private struct MatchDataValuePair(T)
+    # Creates the pair formatter.
+    def initialize(@key : Symbol, @value : T)
+    end
+
+    # Appends the pair to the output.
+    def to_s(io)
+      io << @key
+      io << ": "
+      io << @value
+    end
+  end
+end