"(ert)") or https://www.gnu.org/software/emacs/manual/html_node/ert/
for more information on writing and running tests.
+If your test lasts longer than some few seconds, mark it in its
+'ert-deftest' definition with ":tags '(:expensive-test)".
+
To run tests on the entire Emacs tree, run "make check" from the
top-level directory. Most tests are in the directory
"test/automated". From the "test/automated" directory, run "make
<filename>" to run the tests for <filename>.el(c). See
"test/automated/Makefile" for more information.
+Tests which are tagged ":expensive-test" are enabled additionally, if
+you run "make check-expensive" from the top-level directory. "make
+<filename>" as mentioned above incorporates expensive tests for
+<filename>.el(c). You can also define any ert selector on the command
+line. So "make check SELECTOR=nil" is equivalent to "make
+check-expensive".
+
** Understanding Emacs Internals.
The best way to understand Emacs Internals is to read the code,