"(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/". From the "test/" directory, run "make
<filename>" to run the tests for <filename>.el(c). See
"test/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".
+
+You could also use predefined selectors of the Makefile. "make
+<filename> SELECTOR='$(SELECTOR_DEFAULT)'" runs all tests for
+<filename>.el(c) except the tests tagged as expensive.
+
+Selectors can be defined with different methods, see (info "(ert)Test
+Selectors") or
+https://www.gnu.org/software/emacs/manual/html_node/ert/Test-Selectors.html
+If your test file contains the tests "test-foo", "test2-foo" and
+"test-foo-remote", and you want to run only the former two tests, you
+could use a regexp: "make <filename> SELECTOR='\"foo$$\"'" .
+
** Understanding Emacs Internals.
The best way to understand Emacs Internals is to read the code,