Implement a custom version of assert_receive.

lib/blank_assertions.ex

@@ -33,7 +33,14 @@ defmodule BlankAssertions do
       end
     else
       quote do
-        ExUnit.Assertions.assert_receive(var!(expr), 100)
+        receive do
+          unquote(expr) -> :ok
+        after
+          100 -> {:messages, messages} = Process.info(self(), :messages)
+                mailbox = Enum.map_join(messages, ", ", &inspect/1)
+                message = inspect(unquote(expr))
+                ExUnit.Assertions.flunk("message #{message} not found in [#{mailbox}]")
+        end
       end
     end
   end

lib/display.ex

@@ -1,6 +1,7 @@
 defmodule Display do
   alias IO.ANSI
   @current_dir File.cwd!
+  @no_value :ex_unit_no_meaningful_value
 
   def invalid_koan(koan, modules) do
     koans_names = module_names(modules)
@@ -43,10 +44,18 @@ defmodule Display do
     end
   end
 
+  defp format_failure(%{error: %ExUnit.AssertionError{expr: @no_value, message: message}, file: file, line: line}) do
+    format_assertion_error(message, file, line)
+  end
+
   defp format_failure(%{error: %ExUnit.AssertionError{expr: expr}, file: file, line: line}) do
+    format_assertion_error(expr, file, line)
+  end
+
+  defp format_assertion_error(error, file, line) do
     """
     #{format_cyan("Assertion failed in #{file}:#{line}")}
-    #{format_red(Macro.to_string(expr))}
+    #{format_red(Macro.to_string(error))}
     """
   end