[Offload] Skip most liboffload tests if no devices (llvm#157417)

If there are no devices available for testing on liboffload, the test
will no longer throw an error when it fails to instantiate.

The tests will be silently skipped, but with a warning printed to
stderr.

Author: RossBrunton

offload/unittests/OffloadAPI/common/Environment.cpp

@@ -129,6 +129,9 @@ const std::vector<TestEnvironment::Device> &TestEnvironment::getDevices() {
     }
   }
 
+  if (Devices.size() == 0)
+    errs() << "Warning: No devices found for OffloadAPI tests.\n";
+
   return Devices;
 }
 

offload/unittests/OffloadAPI/common/Fixtures.hpp

@@ -250,9 +250,13 @@ struct OffloadEventTest : OffloadQueueTest {
   ol_event_handle_t Event = nullptr;
 };
 
+// Devices might not be available for offload testing, so allow uninstantiated
+// tests (as the device list will be empty). This means that all tests requiring
+// a device will be silently skipped.
 #define OFFLOAD_TESTS_INSTANTIATE_DEVICE_FIXTURE(FIXTURE)                      \
   INSTANTIATE_TEST_SUITE_P(                                                    \
       , FIXTURE, ::testing::ValuesIn(TestEnvironment::getDevices()),           \
       [](const ::testing::TestParamInfo<TestEnvironment::Device> &info) {      \
         return SanitizeString(info.param.Name);                                \
-      })
+      });                                                                      \
+  GTEST_ALLOW_UNINSTANTIATED_PARAMETERIZED_TEST(FIXTURE)