Use red or green background for whitespace-only diffs (#5476)

Author: josevalim

lib/ex_unit/examples/difference.exs

@@ -25,6 +25,12 @@ defmodule Difference do
     assert string1 == string2
   end
 
+  test "whitespace" do
+    list1 = [%{a: "abc "}, %{a: "def"}, %{c: "gh"}]
+    list2 = [%{a: "abc"}, %{a: " def"}, %{c: "hi"}]
+    assert list1 == list2
+  end
+
   test "large strings" do
     string1 = "short"
     string2 = "really long string that should not emit diff"

lib/ex_unit/lib/ex_unit/cli_formatter.ex

@@ -179,9 +179,13 @@ defmodule ExUnit.CLIFormatter do
   # Color styles
 
   defp colorize(escape, string, %{colors: colors}) do
-    [escape | string]
-    |> IO.ANSI.format(colors[:enabled])
-    |> IO.iodata_to_binary
+    if colors[:enabled] do
+      [escape, string, :reset]
+      |> IO.ANSI.format_fragment(true)
+      |> IO.iodata_to_binary
+    else
+      string
+    end
   end
 
   defp success(msg, config) do
@@ -211,9 +215,15 @@ defmodule ExUnit.CLIFormatter do
   defp formatter(:diff_delete, msg, config),
     do: colorize(:red, msg, config)
 
+  defp formatter(:diff_delete_whitespace, msg, config),
+    do: colorize(IO.ANSI.color_background(2, 0, 0), msg, config)
+
   defp formatter(:diff_insert, msg, config),
     do: colorize(:green, msg, config)
 
+  defp formatter(:diff_insert_whitespace, msg, config),
+    do: colorize(IO.ANSI.color_background(0, 2, 0), msg, config)
+
   defp formatter(_,  msg, _config),
     do: msg
 

lib/ex_unit/lib/ex_unit/formatter.ex

@@ -252,11 +252,17 @@ defmodule ExUnit.Formatter do
   end
 
   defp colorize_diff({:del, content}, formatter, {left, right}) do
-    {[left | formatter.(:diff_delete, content)], right}
+    format = colorize_format(content, :diff_delete, :diff_delete_whitespace)
+    {[left | formatter.(format, content)], right}
   end
 
   defp colorize_diff({:ins, content}, formatter, {left, right}) do
-    {left, [right | formatter.(:diff_insert, content)]}
+    format = colorize_format(content, :diff_insert, :diff_insert_whitespace)
+    {left, [right | formatter.(format, content)]}
+  end
+
+  defp colorize_format(content, normal, whitespace) do
+    if String.trim_leading(content) == "", do: whitespace, else: normal
   end
 
   defp edit_script(left, right) do