Provide error strings if kernel tracing test skipped

Signed-off-by: Christophe Bedard <christophe.bedard@apex.ai>

test_ros2trace/test/test_ros2trace/test_trace.py

@@ -52,6 +52,21 @@ def are_tracepoints_included() -> bool:
     return 0 == process.returncode
 
 
+def skip_if_no_kernel_tracing():
+    kernel_tracepoints = lttngpy.get_tracepoints(domain_type=lttngpy.LTTNG_DOMAIN_KERNEL)
+    syscalls = lttngpy.get_syscalls()
+    error = ', '.join(
+        f'{name}: {lttngpy.lttng_strerror(error_code)}' for name, error_code in (
+            ('kernel tracepoints', kernel_tracepoints),
+            ('syscalls', syscalls),
+        )
+        if isinstance(error_code, int)
+    )
+    if error:
+        return unittest.skip(f'kernel tracer is required: {error}')
+    return lambda test_case: test_case
+
+
 @unittest.skipIf(not is_lttng_installed(minimum_version='2.9.0'), 'LTTng is required')
 class TestROS2TraceCLI(unittest.TestCase):
 
@@ -316,13 +331,7 @@ def test_default_tracing(self) -> None:
 
         shutil.rmtree(tmpdir)
 
-    @unittest.skipIf(
-        (
-            isinstance(lttngpy.get_tracepoints(domain_type=lttngpy.LTTNG_DOMAIN_KERNEL), int) or
-            isinstance(lttngpy.get_syscalls(), int)
-        ),
-        'kernel tracer is required',
-    )
+    @skip_if_no_kernel_tracing()
     def test_kernel_tracing(self) -> None:
         tmpdir = self.create_test_tmpdir('test_kernel_tracing')
         session_name = 'test_kernel_tracing'