* Build
** bootstrapping
Libraries that are part of the "bootstrap set" cannot rely on
autoloading.  Example: =files.el= must ~(eval-when-compile (require
'pcase))~, even though it only uses autoloaded macros.
* Tests
** Running
Somehow I can never remember how to ask =make= how to run a specific
set of tests.

tl;dr, running =$testcases_regexp= from =test/$testfile.el=, to test
changes in =lisp/$sourcefile.el=:
#+begin_src sh
make -C test $testfile \
     TEST_LOAD_EL=yes \
     TEST_BACKTRACE_LINE_LENGTH=nil \
     SELECTOR="\"$testcases_regexp\"" \
     EMACS_EXTRAOPT="-l ../lisp/$sourcefile.el"
#+end_src

Relevant bits from test/Makefile:

#+begin_src makefile
## filename.log: run tests from filename.el(c) if .log file needs updating
## filename: re-run tests from filename.el(c), with no logging
#+end_src

#+begin_src makefile
# Whether to run tests from .el files in preference to .elc, we do
# this by default since it gives nicer stacktraces.
# If you just want a pass/fail, setting this to no is much faster.
export TEST_LOAD_EL ?= \
    $(if $(findstring $(MAKECMDGOALS), all check check-maybe),no,yes)
#+end_src

#+begin_src makefile
TEST_RUN_ERT = --batch --eval '(ert-run-tests-batch-and-exit (quote ${SELECTOR_ACTUAL}))' ${WRITE_LOG}
#+end_src

#+begin_src makefile
ifdef SELECTOR
SELECTOR_ACTUAL=$(SELECTOR)
#+end_src

Selector documentation from ~ert-select-tests~:
#+begin_quote
Valid SELECTORs:

nil  -- Selects the empty set.
t    -- Selects UNIVERSE.
:new -- Selects all tests that have not been run yet.
:failed, :passed       -- Select tests according to their most recent result.
:expected, :unexpected -- Select tests according to their most recent result.
a string -- A regular expression selecting all tests with matching names.
a test   -- (i.e., an object of the ert-test data-type) Selects that test.
a symbol -- Selects the test that the symbol names, signals an
    ‘ert-test-unbound’ error if none.
(member TESTS...) -- Selects the elements of TESTS, a list of tests
    or symbols naming tests.
(eql TEST) -- Selects TEST, a test or a symbol naming a test.
(and SELECTORS...) -- Selects the tests that match all SELECTORS.
(or SELECTORS...)  -- Selects the tests that match any of the SELECTORS.
(not SELECTOR)     -- Selects all tests that do not match SELECTOR.
(tag TAG) -- Selects all tests that have TAG on their tags list.
    A tag is an arbitrary label you can apply when you define a test.
(satisfies PREDICATE) -- Selects all tests that satisfy PREDICATE.
    PREDICATE is a function that takes an ert-test object as argument,
    and returns non-nil if it is selected.
#+end_quote
** Writing
*** Mocking functions
#+begin_src elisp
(cl-letf (((symbol-function 'read-something)
           (lambda (&rest _) "result")))
  (some-command))
#+end_src

* Third-party packages
** forge
*** build
Use =config.mk= to set =LOAD_PATH=:
#+begin_src makefile
find-lib = $(dir $(shell emacs -Q -batch                \
	-eval "(require 'find-func)"                    \
	-eval "(package-initialize)"                    \
	-eval "(require '$(1))"                         \
	-eval "(princ (find-library-name \"$(1)\"))"))

sources = ~/src/emacs/magit/lisp

elpa =                                          \
	closql                                  \
	compat                                  \
	dash                                    \
	emacsql                                 \
	ghub                                    \
	markdown-mode                           \
	transient                               \
	treepy                                  \
	with-editor                             \
	yaml
elpa_dirs = $(foreach d,$(elpa),$(call find-lib,$(d)))

LOAD_PATH = $(addprefix -L ,$(elpa_dirs) $(sources))
#+end_src

*** load sources
~emacs -Q -L ./lisp~ does not seem to work: after running
~(package-initialize)~, =M-x find-library forge= returns the instance
installed under ~package-user-dir~.

This can be circumvented with ~(setq pacakge-load-list '((forge nil)
all))~.

Full command line for easy startup:

#+begin_src sh
emacs -Q -L ./lisp \
      -eval "(setq pacakge-load-list '((forge nil) all))" \
      -f package-initialize \
#+end_src