lol this is what i get for using private apis

test/support/style_case.ex

@@ -131,32 +131,39 @@ defmodule Styler.StyleCase do
     end
   end
 
-  def format_diff(left, right, prelude \\ "Styling produced unexpected results") do
-    # reaching into private ExUnit stuff, uh oh!
-    # this gets us the nice diffing from ExUnit while allowing us to print our code blocks as strings rather than inspected strings
-    {%{left: left, right: right}, _} = ExUnit.Diff.compute(left, right, :==)
-    left = for {diff?, content} <- left.contents, do: if(diff?, do: [:red, content, :reset], else: content)
-    right = for {diff?, content} <- right.contents, do: if(diff?, do: [:green, content, :reset], else: content)
-    header = IO.ANSI.format([:red, prelude, :reset])
-
-    left =
-      [[:cyan, "left:\n", :reset] | left]
-      |> IO.ANSI.format()
-      |> to_string()
-      |> Macro.unescape_string()
-      |> String.replace("\n", "\n  ")
-
-    right =
-      [[:cyan, "right:\n", :reset] | right]
-      |> IO.ANSI.format()
-      |> to_string()
-      |> Macro.unescape_string()
-      |> String.replace("\n", "\n  ")
-
-    """
-    #{header}
-    #{left}
-    #{right}
-    """
+  if Version.match?(System.version(), ">= 1.15.0-dev") do
+    def format_diff(left, right, prelude \\ "Styling produced unexpected results") do
+      # reaching into private ExUnit stuff, uh oh!
+      # this gets us the nice diffing from ExUnit while allowing us to print our code blocks as strings rather than inspected strings
+      {%{left: left, right: right}, _} = ExUnit.Diff.compute(left, right, :==)
+      left = for {diff?, content} <- left.contents, do: if(diff?, do: [:red, content, :reset], else: content)
+      right = for {diff?, content} <- right.contents, do: if(diff?, do: [:green, content, :reset], else: content)
+      header = IO.ANSI.format([:red, prelude, :reset])
+
+      left =
+        [[:cyan, "left:\n", :reset] | left]
+        |> IO.ANSI.format()
+        |> to_string()
+        |> Macro.unescape_string()
+        |> String.replace("\n", "\n  ")
+
+      right =
+        [[:cyan, "right:\n", :reset] | right]
+        |> IO.ANSI.format()
+        |> to_string()
+        |> Macro.unescape_string()
+        |> String.replace("\n", "\n  ")
+
+      """
+      #{header}
+      #{left}
+      #{right}
+      """
+    end
+  else
+    def format_diff(left, right, prelude \\ "") do
+      IO.puts(prelude)
+      assert left == right
+    end
   end
 end