lib: allow igt_skip_on_simulation outside of fixtures.

Thomas noticed that in simulation mode a lot of the tests fall over
instead of skipping properly. This is due to recently added
self-checks which ensure that any call to igt_skip happens either
within a fixture or subtest block (or it's a simple test without
subtests). This is to catch bugs since pretty much always not wrapping
up hardware setup and checks into these blocks is a bug.

Bug simulation skipping is a bit different, so allow that exception.
Otherwise we'd need to fix up piles of tests (and likely need to play
a game of whack-a-mole).

Also add a library testcase for all the different variants to make
sure it really works.

Cc: Thomas Wood <thomas.wood@intel.com>
Cc: Ben Widawsky <benjamin.widawsky@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

lib/igt_core.c

@@ -1117,13 +1117,23 @@ bool igt_run_in_simulation(void)
  *
  * Skip tests when INTEL_SIMULATION environment variable is set. It uses
  * igt_skip() internally and hence is fully subtest aware.
+ *
+ * Note that in contrast to all other functions which use igt_skip() internally
+ * it is allowed to use this outside of an #igt_fixture block in a test with
+ * subtests. This is because in contrast to most other test requirements,
+ * checking for simulation mode doesn't depend upon the present hardware and it
+ * so makes a lot of sense to have this check in the outermost #igt_main block.
  */
 void igt_skip_on_simulation(void)
 {
 	if (igt_only_list_subtests())
 		return;
 
-	igt_require(!igt_run_in_simulation());
+	if (!in_fixture) {
+		igt_fixture
+			igt_require(!igt_run_in_simulation());
+	} else
+		igt_require(!igt_run_in_simulation());
 }
 
 /* structured logging */