test-tool run-command testsuite: get shell from env

When running tests through `test-tool run-command testsuite`, we
currently hardcode `sh` as the command interpreter. As discussed in [1],
this is incorrect, and we should be using the shell set in
TEST_SHELL_PATH instead.

Add a shell_path field in struct testsuite so that we can pass this to
the task runner callback. If this is non-null, we'll use it as the
argv[0] of the subprocess. Otherwise, we'll just execute the test
program directly. We will use this feature in a later commit to enable
running binary executable unit tests.

However, for now when setting up the struct testsuite in testsuite(),
use the value of TEST_SHELL_PATH if it's set, otherwise keep the
original behavior by defaulting to `sh`.

[1] https://lore.kernel.org/git/[email protected]/

Signed-off-by: Josh Steadmon <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: steadmon

t/helper/test-run-command.c

@@ -65,6 +65,7 @@ struct testsuite {
 	struct string_list tests, failed;
 	int next;
 	int quiet, immediate, verbose, verbose_log, trace, write_junit_xml;
+	const char *shell_path;
 };
 #define TESTSUITE_INIT { \
 	.tests = STRING_LIST_INIT_DUP, \
@@ -80,7 +81,9 @@ static int next_test(struct child_process *cp, struct strbuf *err, void *cb,
 		return 0;
 
 	test = suite->tests.items[suite->next++].string;
-	strvec_pushl(&cp->args, "sh", test, NULL);
+	if (suite->shell_path)
+		strvec_push(&cp->args, suite->shell_path);
+	strvec_push(&cp->args, test);
 	if (suite->quiet)
 		strvec_push(&cp->args, "--quiet");
 	if (suite->immediate)
@@ -162,6 +165,10 @@ static int testsuite(int argc, const char **argv)
 	if (max_jobs <= 0)
 		max_jobs = online_cpus();
 
+	suite.shell_path = getenv("TEST_SHELL_PATH");
+	if (!suite.shell_path)
+		suite.shell_path = "sh";
+
 	dir = opendir(".");
 	if (!dir)
 		die("Could not open the current directory");