tests: add 'test_bool_env' to catch non-bool GIT_TEST_* values

Since 3b072c577b (tests: replace test_tristate with "git env--helper",
2019-06-21) we get the normalized bool values of various GIT_TEST_*
environment variables via 'git env--helper'.  Now, while the 'git
env--helper' command itself does catch invalid values in the
environment variable or in the given --default and exits with error
(exit code 128 or 129, respectively), it's invoked in conditions like
'if ! git env--helper ...', which means that all invalid bool values
are interpreted the same as the ordinary 'false' (exit code 1).  This
has led to inadvertently skipped httpd tests in our CI builds for a
couple of weeks, see 3960290675 (ci: restore running httpd tests,
2019-09-06).

Let's be more careful about what the test suite accepts as bool values
in GIT_TEST_* environment variables, and error out loud and clear on
invalid values instead of simply skipping tests.  Add the
'test_bool_env' helper function to encapsulate the invocation of 'git
env--helper' and the verification of its exit code, and replace all
invocations of that command in our test framework and test suite with
a call to this new helper (except in 't0017-env-helper.sh', of
course).

  $ GIT_TEST_GIT_DAEMON=YesPlease ./t5570-git-daemon.sh
  fatal: bad numeric config value 'YesPlease' for 'GIT_TEST_GIT_DAEMON': invalid unit
  error: test_bool_env requires bool values both for $GIT_TEST_GIT_DAEMON and for the default fallback

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/README

@@ -978,6 +978,15 @@ library for your script to use.
    output to the downstream---unlike the real version, it generates
    only up to 99 lines.
 
+ - test_bool_env <env-variable-name> <default-value>
+
+   Given the name of an environment variable with a bool value,
+   normalize its value to a 0 (true) or 1 (false or empty string)
+   return code.  Return with code corresponding to the given default
+   value if the variable is unset.
+   Abort the test script if either the value of the variable or the
+   default are not valid bool values.
+
 
 Prerequisites
 -------------

t/lib-git-daemon.sh

@@ -15,7 +15,7 @@
 #
 #	test_done
 
-if ! git env--helper --type=bool --default=true --exit-code GIT_TEST_GIT_DAEMON
+if ! test_bool_env GIT_TEST_GIT_DAEMON true
 then
 	skip_all="git-daemon testing disabled (unset GIT_TEST_GIT_DAEMON to enable)"
 	test_done

t/lib-git-svn.sh

@@ -69,7 +69,7 @@ svn_cmd () {
 maybe_start_httpd () {
 	loc=${1-svn}
 
-	if git env--helper --type=bool --default=false --exit-code GIT_TEST_SVN_HTTPD
+	if test_bool_env GIT_TEST_SVN_HTTPD false
 	then
 		. "$TEST_DIRECTORY"/lib-httpd.sh
 		LIB_HTTPD_SVN="$loc"
@@ -104,7 +104,7 @@ EOF
 }
 
 require_svnserve () {
-	if ! git env--helper --type=bool --default=false --exit-code GIT_TEST_SVNSERVE
+	if ! test_bool_env GIT_TEST_SVNSERVE false
 	then
 		skip_all='skipping svnserve test. (set $GIT_TEST_SVNSERVE to enable)'
 		test_done

t/lib-httpd.sh

@@ -41,7 +41,7 @@ then
 	test_done
 fi
 
-if ! git env--helper --type=bool --default=true --exit-code GIT_TEST_HTTPD
+if ! test_bool_env GIT_TEST_HTTPD true
 then
 	skip_all="Network testing disabled (unset GIT_TEST_HTTPD to enable)"
 	test_done

t/t0000-basic.sh

@@ -916,6 +916,40 @@ test_expect_success 'test_oid can look up data for SHA-256' '
 	test "$hexsz" -eq 64
 '
 
+test_expect_success 'test_bool_env' '
+	(
+		sane_unset envvar &&
+
+		test_bool_env envvar true &&
+		! test_bool_env envvar false &&
+
+		envvar= &&
+		export envvar &&
+		! test_bool_env envvar true &&
+		! test_bool_env envvar false &&
+
+		envvar=true &&
+		test_bool_env envvar true &&
+		test_bool_env envvar false &&
+
+		envvar=false &&
+		! test_bool_env envvar true &&
+		! test_bool_env envvar false &&
+
+		envvar=invalid &&
+		# When encountering an invalid bool value, test_bool_env
+		# prints its error message to the original stderr of the
+		# test script, hence the redirection of fd 7, and aborts
+		# with "exit 1", hence the subshell.
+		! ( test_bool_env envvar true ) 7>err &&
+		grep "error: test_bool_env requires bool values" err &&
+
+		envvar=true &&
+		! ( test_bool_env envvar invalid ) 7>err &&
+		grep "error: test_bool_env requires bool values" err
+	)
+'
+
 ################################################################
 # Basics of the basics
 

t/t5512-ls-remote.sh

@@ -267,7 +267,7 @@ test_expect_success 'ls-remote --symref omits filtered-out matches' '
 '
 
 test_lazy_prereq GIT_DAEMON '
-	git env--helper --type=bool --default=true --exit-code GIT_TEST_GIT_DAEMON
+	test_bool_env GIT_TEST_GIT_DAEMON true
 '
 
 # This test spawns a daemon, so run it only if the user would be OK with

t/test-lib-functions.sh

@@ -1175,6 +1175,34 @@ perl () {
 	command "$PERL_PATH" "$@" 2>&7
 } 7>&2 2>&4
 
+# Given the name of an environment variable with a bool value, normalize
+# its value to a 0 (true) or 1 (false or empty string) return code.
+#
+#   test_bool_env GIT_TEST_HTTPD <default-value>
+#
+# Return with code corresponding to the given default value if the variable
+# is unset.
+# Abort the test script if either the value of the variable or the default
+# are not valid bool values.
+
+test_bool_env () {
+	if test $# != 2
+	then
+		BUG "test_bool_env requires two parameters (variable name and default value)"
+	fi
+
+	git env--helper --type=bool --default="$2" --exit-code "$1"
+	ret=$?
+	case $ret in
+	0|1)	# unset or valid bool value
+		;;
+	*)	# invalid bool value or something unexpected
+		error >&7 "test_bool_env requires bool values both for \$$1 and for the default fallback"
+		;;
+	esac
+	return $ret
+}
+
 # Exit the test suite, either by skipping all remaining tests or by
 # exiting with an error. If our prerequisite variable $1 falls back
 # on a default assume we were opportunistically trying to set up some
@@ -1183,7 +1211,7 @@ perl () {
 # The error/skip message should be given by $2.
 #
 test_skip_or_die () {
-	if ! git env--helper --type=bool --default=false --exit-code $1
+	if ! test_bool_env "$1" false
 	then
 		skip_all=$2
 		test_done

t/test-lib.sh

@@ -1406,19 +1406,19 @@ yes () {
 # The GIT_TEST_FAIL_PREREQS code hooks into test_set_prereq(), and
 # thus needs to be set up really early, and set an internal variable
 # for convenience so the hot test_set_prereq() codepath doesn't need
-# to call "git env--helper". Only do that work if needed by seeing if
+# to call "git env--helper" (via test_bool_env). Only do that work
-# GIT_TEST_FAIL_PREREQS is set at all.
+# if needed by seeing if GIT_TEST_FAIL_PREREQS is set at all.
 GIT_TEST_FAIL_PREREQS_INTERNAL=
 if test -n "$GIT_TEST_FAIL_PREREQS"
 then
-	if git env--helper --type=bool --default=0 --exit-code GIT_TEST_FAIL_PREREQS
+	if test_bool_env GIT_TEST_FAIL_PREREQS false
 	then
 		GIT_TEST_FAIL_PREREQS_INTERNAL=true
 		test_set_prereq FAIL_PREREQS
 	fi
 else
 	test_lazy_prereq FAIL_PREREQS '
-		git env--helper --type=bool --default=0 --exit-code GIT_TEST_FAIL_PREREQS
+		test_bool_env GIT_TEST_FAIL_PREREQS false
 	'
 fi
 
@@ -1477,7 +1477,7 @@ then
 fi
 
 test_lazy_prereq C_LOCALE_OUTPUT '
-	! git env--helper --type=bool --default=0 --exit-code GIT_TEST_GETTEXT_POISON
+	! test_bool_env GIT_TEST_GETTEXT_POISON false
 '
 
 if test -z "$GIT_TEST_CHECK_CACHE_TREE"