diag ... failed
  % 'btest-diff output' failed unexpectedly (exit code 100)
  % cat .diag
  == File ===============================
  Hello, World!
  == Error ===============================
  test-diff: no baseline found.
  =======================================

  % cat .stderr

1 of 1 test failed
diag ... failed
  % 'btest-diff output' failed unexpectedly (exit code 1)
  % cat .diag
  == File ===============================
  Hello, World!
  == Diff ===============================
  @@ -1 +1 @@
  -Wrong baseline
  +Hello, World!
  =======================================

  % cat .stderr

1 of 1 test failed
