test: Add a way to detect a test that breaks another

When running unit tests, some may have side effects which cause a
subsequent test to break. This can sometimes be seen when using 'ut dm'
or similar.

Add a new argument which allows a particular (failing) test to be run
immediately after a certain number of tests have run. This allows the
test causing the failure to be determined.

Update the documentation also.

Signed-off-by: Simon Glass <sjg@chromium.org>

6 files changed, 127 insertions, 10 deletions

diff --git a/arch/sandbox/cpu/spl.c b/arch/sandbox/cpu/spl.c
index 0faf34cc00..09e3d10d6a 100644
--- a/arch/sandbox/cpu/spl.c
+++ b/arch/sandbox/cpu/spl.c
@@ -132,7 +132,7 @@ void spl_board_init(void)
 		int ret;
 
 		ret = ut_run_list("spl", NULL, tests, count,
-				  state->select_unittests, 1, false);
+				  state->select_unittests, 1, false, NULL);
 		/* continue execution into U-Boot */
 	}
 }
diff --git a/doc/develop/tests_sandbox.rst b/doc/develop/tests_sandbox.rst
index 8e42a32afb..bfd3bdb927 100644
--- a/doc/develop/tests_sandbox.rst
+++ b/doc/develop/tests_sandbox.rst
@@ -143,6 +143,75 @@ For example::
    Test dm_test_rtc_reset failed 3 times
 
 
+Isolating a test that breaks another
+------------------------------------
+
+When running unit tests, some may have side effects which cause a subsequent
+test to break. This can sometimes be seen when using 'ut dm' or similar.
+
+You can use the `-I` argument to the `ut` command to isolate this problem.
+First use `ut info` to see how many tests there are, then use a binary search to
+home in on the problem. Note that you might need to restart U-Boot after each
+iteration, so the `-c` argument to U-Boot is useful.
+
+For example, let's stay that dm_test_host() is failing::
+
+   => ut dm
+   ...
+   Test: dm_test_get_stats: core.c
+   Test: dm_test_get_stats: core.c (flat tree)
+   Test: dm_test_host: host.c
+   test/dm/host.c:71, dm_test_host(): 0 == ut_check_delta(mem_start): Expected 0x0 (0), got 0xffffcbb0 (-13392)
+   Test: dm_test_host: host.c (flat tree)
+   Test <NULL> failed 1 times
+   Test: dm_test_host_dup: host.c
+   Test: dm_test_host_dup: host.c (flat tree)
+   ...
+
+You can then tell U-Boot to run the failing test at different points in the
+sequence:
+
+   => ut info
+   Test suites: 21
+   Total tests: 645
+
+::
+
+   $ ./u-boot -T -c "ut dm -I300:dm_test_host"
+   ...
+   Test: dm_test_pinctrl_single: pinmux.c (flat tree)
+   Test: dm_test_host: host.c
+   test/dm/host.c:71, dm_test_host(): 0 == ut_check_delta(mem_start): Expected 0x0 (0), got 0xfffffdb0 (-592)
+   Test: dm_test_host: host.c (flat tree)
+   Test dm_test_host failed 1 times (position 300)
+   Failures: 4
+
+So it happened before position 300. Trying 150 shows it failing, so we try 75::
+
+   $ ./u-boot  -T  -c "ut dm -I75:dm_test_host"
+   ...
+   Test: dm_test_autoprobe: core.c
+   Test: dm_test_autoprobe: core.c (flat tree)
+   Test: dm_test_host: host.c
+   Test: dm_test_host: host.c (flat tree)
+   Failures: 0
+
+That succeeds, so we try 120, etc. until eventually we can figure out that the
+problem first happens at position 82.
+
+   $ ./u-boot  -T  -c "ut dm -I82:dm_test_host"
+   ...
+   Test: dm_test_blk_flags: blk.c
+   Test: dm_test_blk_flags: blk.c (flat tree)
+   Test: dm_test_host: host.c
+   test/dm/host.c:71, dm_test_host(): 0 == ut_check_delta(mem_start): Expected 0x0 (0), got 0xffffc960 (-13984)
+   Test: dm_test_host: host.c (flat tree)
+   Test dm_test_host failed 1 times (position 82)
+   Failures: 1
+
+From this we can deduce that `dm_test_blk_flags()` causes the problem with
+`dm_test_host()`.
+
 Running sandbox_spl tests directly
 ----------------------------------
 
diff --git a/doc/usage/cmd/ut.rst b/doc/usage/cmd/ut.rst
index 11c64a1779..a3039634f2 100644
--- a/doc/usage/cmd/ut.rst
+++ b/doc/usage/cmd/ut.rst
@@ -8,10 +8,12 @@ Synopis
 
 ::
 
-    ut [-r<runs>] [-f] [<suite> [<test>]]
+    ut [-r<runs>] [-f] [-I<n>:<one_test>] [<suite> [<test>]]
 
        <runs>      Number of times to run each test
        -f          Force 'manual' tests to run as well
+       <n>         Run <one test> after <n> other tests have run
+       <one_test>  Name of the 'one' test to run
        <suite>     Test suite to run, or `all`
        <test>      Name of single test to run
 
@@ -35,6 +37,13 @@ Manual tests are normally skipped by this command. Use `-f` to run them. See
 See :ref:`develop/tests_writing:mixing python and c` for more information on
 manual test.
 
+When running unit tests, some may have side effects which cause a subsequent
+test to break. This can sometimes be seen when using 'ut dm' or similar. To
+fix this, select the 'one' test which breaks. Then tell the 'ut' command to
+run this one test after a certain number of other tests have run. Using a
+binary search method with `-I` you can quickly figure one which test is causing
+the problem.
+
 Generally all tests in the suite are run. To run just a single test from the
 suite, provide the <test> argument.
 
diff --git a/include/test/ut.h b/include/test/ut.h
index e0e618b58c..4d00b4eeca 100644
--- a/include/test/ut.h
+++ b/include/test/ut.h
@@ -410,10 +410,15 @@ void test_set_state(struct unit_test_state *uts);
  *	then all tests are run
  * @runs_per_test: Number of times to run each test (typically 1)
  * @force_run: Run tests that are marked as manual-only (UT_TESTF_MANUAL)
+ * @test_insert: String describing a test to run after n other tests run, in the
+ * format n:name where n is the number of tests to run before this one and
+ * name is the name of the test to run. This is used to find which test causes
+ * another test to fail. If the one test fails, testing stops immediately.
+ * Pass NULL to disable this
  * Return: 0 if all tests passed, -1 if any failed
  */
 int ut_run_list(const char *name, const char *prefix, struct unit_test *tests,
 		int count, const char *select_name, int runs_per_test,
-		bool force_run);
+		bool force_run, const char *test_insert);
 
 #endif
diff --git a/test/cmd_ut.c b/test/cmd_ut.c
index 76e37f35c8..2736582f11 100644
--- a/test/cmd_ut.c
+++ b/test/cmd_ut.c
@@ -21,6 +21,7 @@ int cmd_ut_category(const char *name, const char *prefix,
 		    struct unit_test *tests, int n_ents,
 		    int argc, char *const argv[])
 {
+	const char *test_insert = NULL;
 	int runs_per_text = 1;
 	bool force_run = false;
 	int ret;
@@ -35,13 +36,17 @@ int cmd_ut_category(const char *name, const char *prefix,
 		case 'f':
 			force_run = true;
 			break;
+		case 'I':
+			test_insert = str + 2;
+			break;
 		}
 		argv++;
-		argc++;
+		argc--;
 	}
 
 	ret = ut_run_list(name, prefix, tests, n_ents,
-			  argc > 1 ? argv[1] : NULL, runs_per_text, force_run);
+			  argc > 1 ? argv[1] : NULL, runs_per_text, force_run,
+			  test_insert);
 
 	return ret ? CMD_RET_FAILURE : 0;
 }
diff --git a/test/test-main.c b/test/test-main.c
index ab3b00a3b3..5931e94a91 100644
--- a/test/test-main.c
+++ b/test/test-main.c
@@ -498,12 +498,29 @@ static int ut_run_test_live_flat(struct unit_test_state *uts,
  */
 static int ut_run_tests(struct unit_test_state *uts, const char *prefix,
 			struct unit_test *tests, int count,
-			const char *select_name)
+			const char *select_name, const char *test_insert)
 {
-	struct unit_test *test;
+	struct unit_test *test, *one;
 	int found = 0;
+	int pos = 0;
+	int upto;
 
-	for (test = tests; test < tests + count; test++) {
+	one = NULL;
+	if (test_insert) {
+		char *p;
+
+		pos = dectoul(test_insert, NULL);
+		p = strchr(test_insert, ':');
+		if (p)
+			p++;
+
+		for (test = tests; test < tests + count; test++) {
+			if (!strcmp(p, test->name))
+				one = test;
+		}
+	}
+
+	for (upto = 0, test = tests; test < tests + count; test++, upto++) {
 		const char *test_name = test->name;
 		int ret, i, old_fail_count;
 
@@ -534,6 +551,17 @@ static int ut_run_tests(struct unit_test_state *uts, const char *prefix,
 			}
 		}
 		old_fail_count = uts->fail_count;
+
+		if (one && upto == pos) {
+			ret = ut_run_test_live_flat(uts, one);
+			if (uts->fail_count != old_fail_count) {
+				printf("Test %s failed %d times (position %d)\n",
+				       one->name,
+				       uts->fail_count - old_fail_count, pos);
+			}
+			return -EBADF;
+		}
+
 		for (i = 0; i < uts->runs_per_test; i++)
 			ret = ut_run_test_live_flat(uts, test);
 		if (uts->fail_count != old_fail_count) {
@@ -554,7 +582,7 @@ static int ut_run_tests(struct unit_test_state *uts, const char *prefix,
 
 int ut_run_list(const char *category, const char *prefix,
 		struct unit_test *tests, int count, const char *select_name,
-		int runs_per_test, bool force_run)
+		int runs_per_test, bool force_run, const char *test_insert)
 {
 	struct unit_test_state uts = { .fail_count = 0 };
 	bool has_dm_tests = false;
@@ -589,7 +617,8 @@ int ut_run_list(const char *category, const char *prefix,
 		memcpy(uts.fdt_copy, gd->fdt_blob, uts.fdt_size);
 	}
 	uts.force_run = force_run;
-	ret = ut_run_tests(&uts, prefix, tests, count, select_name);
+	ret = ut_run_tests(&uts, prefix, tests, count, select_name,
+			   test_insert);
 
 	/* Best efforts only...ignore errors */
 	if (has_dm_tests)