Add padding to pairs to right-align key

src/spectator/formatting/match_data_value_pair.cr

@@ -2,11 +2,12 @@ module Spectator::Formatting
   # 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)
+    def initialize(@key : Symbol, @value : T, @padding : Int32)
     end
 
     # Appends the pair to the output.
     def to_s(io)
+      @padding.times { io << ' ' }
       io << @key
       io << ": "
       @value.inspect(io)

src/spectator/formatting/match_data_values.cr

@@ -4,14 +4,19 @@ module Spectator::Formatting
   private struct MatchDataValues(T)
     include Enumerable(MatchDataValuePair)
 
+    @max_key_length : Int32
+
     # Creates the values mapper.
     def initialize(@values : T)
+      @max_key_length = T.types.keys.map(&.to_s.size).max
     end
 
     # Yields pairs that can be printed to output.
     def each
       @values.each do |key, value|
-        yield MatchDataValuePair.new(key, value)
+        key_length = key.to_s.size
+        padding = @max_key_length - key_length
+        yield MatchDataValuePair.new(key, value, padding)
       end
     end
   end