How to get current file name when running under ERT?

Question

I have a set of tests that involve loading files from the file-system and I would like to use the current filename to locate the test files relative to the test file.

The below code shows the pattern I am trying, but unfortunately when I run the test using M-x ert, it fails with (wrong-type-argument stringp nil), because both the load-file-name and buffer-file-name are nil. How should I approach this?

(ert-deftest closing-braces ()
  (find-file (concat (file-name-directory
                       (or load-file-name buffer-file-name))
                     "ClosingBrace.file"))
  ...
  )

Answer 1

A wild guess: put the file name in a defvar or a defconst, and use it in the function:

(defconst my-test-location (file-name-directory (or load-file-name buffer-file-name)))

(ert-deftest closing-braces ()
  (find-file (concat my-test-location "ClosingBrace.file")))

What you want is the value of load-file-name or buffer-file-name at compile/load time, but when you reference it within your function (ert-deftest is a fancy version of defun), you get the value at run time, which is not as useful. With defvar or defconst, you should be able to "lock in" the compile/load time value.

Answer 2

I've used the following construct:

(defvar objc-font-lock-test-setup-directory
  (if load-file-name
      (file-name-directory load-file-name)
   default-directory))

It works both when the file is loaded or when doing something like an eval-buffer.