Better formatting for empty arguments

spec/spectator/mocks/arguments_spec.cr

@@ -30,6 +30,14 @@ Spectator.describe Spectator::Arguments do
     it "formats the arguments" do
       is_expected.to eq("(42, \"foo\", bar: \"baz\", qux: 123)")
     end
+
+    context "when empty" do
+      let(arguments) { Spectator::Arguments.empty }
+
+      it "returns (no args)" do
+        is_expected.to eq("(no args)")
+      end
+    end
   end
 
   describe "#==" do

src/spectator/mocks/arguments.cr

@@ -29,6 +29,8 @@ module Spectator
 
     # Constructs a string representation of the arguments.
     def to_s(io : IO) : Nil
+      return io << "(no args)" if args.empty? && kwargs.empty?
+
       io << '('
 
       # Add the positional arguments.