eclass/tests: add Makefile to run eclass tests

Thanks to robbat2 for providing feedback.

Closes: https://github.com/gentoo/gentoo/pull/30603
Signed-off-by: Florian Schmaus <flow@gentoo.org>

.gitignore

@@ -1,6 +1,8 @@
 /.ebuild.x
 /distfiles/
 /eclass/*.5
+/eclass/tests/*.sh.ok
+/eclass/tests/.eclasssum
 /local/
 /packages/
 /profiles/use.local.desc

eclass/tests/Makefile

@@ -0,0 +1,27 @@
+SH_FILES := $(wildcard *.sh)
+TEST_FILES := $(filter-out tests-common.sh, $(SH_FILES))
+TEST_OK_FILES := $(patsubst %.sh, .%.sh.ok,$ $(TEST_FILES))
+
+# We cache a successful test result if the testfile itself did not
+# change (%.sh) and the contents of the eclass/ directory did not
+# change (.eclasssum).
+.%.sh.ok: %.sh .eclasssum
+	./$<
+	touch $@
+
+.PHONY: test
+test: $(TEST_OK_FILES)
+
+.PHONY: force
+.ONESHELL:
+.eclasssum: SHELL = /bin/bash
+.eclasssum: force
+	set -euo pipefail
+	find .. -maxdepth 1 -type f -name "*.eclass" \
+		-exec stat --format="%n %y" \{} \+ |\
+		sort |\
+		cksum -	> $@.cur
+	trap "rm -f $@.cur" EXIT
+	if ! cmp --silent $@.cur $@; then
+		mv $@.cur $@
+	fi