diff --git a/test/msgpax/ext_test.exs b/test/msgpax/ext_test.exs
index 4990a1b..9fed278 100644
--- a/test/msgpax/ext_test.exs
+++ b/test/msgpax/ext_test.exs
@@ -38,27 +38,27 @@ defmodule Msgpax.ExtTest do
 
   test "fixext 1" do
     data = Sample.new("A", 1)
-    assert_format data, <<0xD4, 42, 65>>, {data, [ext: Sample]}
+    assert_format data, <<0xD4, 42, ?A>>, {data, [ext: Sample]}
   end
 
   test "fixext 2" do
     data = Sample.new("B", 2)
-    assert_format data, <<0xD5, 42, 66>>, {data, [ext: Sample]}
+    assert_format data, <<0xD5, 42, ?B>>, {data, [ext: Sample]}
   end
 
   test "fixext 4" do
     data = Sample.new("C", 4)
-    assert_format data, <<0xD6, 42, 67>>, {data, [ext: Sample]}
+    assert_format data, <<0xD6, 42, ?C>>, {data, [ext: Sample]}
   end
 
   test "fixext 8" do
     data = Sample.new("D", 8)
-    assert_format data, <<0xD7, 42, 68>>, {data, [ext: Sample]}
+    assert_format data, <<0xD7, 42, ?D>>, {data, [ext: Sample]}
   end
 
   test "fixext 16" do
     data = Sample.new("E", 16)
-    assert_format data, <<0xD8, 42, 69>>, {data, [ext: Sample]}
+    assert_format data, <<0xD8, 42, ?E>>, {data, [ext: Sample]}
   end
 
   test "ext 8" do
@@ -66,34 +66,33 @@ defmodule Msgpax.ExtTest do
     output = Sample.new("", 0)
     assert_format input, <<0xC7, 0, 42>>, {output, [ext: Sample]}
     data = Sample.new("1", 255)
-    assert_format data, <<0xC7, 255, 42, 49>>, {data, [ext: Sample]}
+    assert_format data, <<0xC7, 255, 42, ?1>>, {data, [ext: Sample]}
   end
 
   test "ext 16" do
     data = Sample.new("2", 0x100)
-    assert_format data, <<0xC8, 0x100::16, 42, 50>>, {data, [ext: Sample]}
+    assert_format data, <<0xC8, 0x100::16, 42, ?2>>, {data, [ext: Sample]}
     data = Sample.new("3", 0xFFFF)
-    assert_format data, <<0xC8, 0xFFFF::16, 42, 51>>, {data, [ext: Sample]}
+    assert_format data, <<0xC8, 0xFFFF::16, 42, ?3>>, {data, [ext: Sample]}
   end
 
   test "ext 32" do
     data = Sample.new("4", 0x10000)
-    assert_format data, <<0xC9, 0x10000::32, 42, 52>>, {data, [ext: Sample]}
+    assert_format data, <<0xC9, 0x10000::32, 42, ?4>>, {data, [ext: Sample]}
   end
 
   test "empty options" do
-    input = Sample.new("A", 1)
-    output = Msgpax.Ext.new(42, "A")
-    assert_format input, <<0xD4, 42, 65>>, output
+    output = Msgpax.Ext.new(42, "G")
+    assert_format Sample.new("G", 1), <<0xD4, 42, ?G>>, output
   end
 
   test "broken ext" do
-    assert {:error, %UnpackError{reason: reason}} = Msgpax.unpack(<<0xD4, 42, 65>>, ext: Broken)
+    assert {:error, %UnpackError{reason: reason}} = Msgpax.unpack(<<0xD4, 42, ?A>>, ext: Broken)
     assert reason == {:ext_unpack_failure, Broken, Msgpax.Ext.new(42, "A")}
   end
 
   test "not supported reserved ext type" do
-    assert {:ok, result} = Msgpax.unpack(<<0xD4, -5, 65>>)
+    assert {:ok, result} = Msgpax.unpack(<<0xD4, -5, ?A>>)
     assert result == %Msgpax.ReservedExt{data: "A", type: -5}
   end
 end