@@ -547,8 +547,8 @@ def subprocess_test_runner(self, test_module, test_class=None,
                    f'captured stderr: {status.stderr}')
         self.assertEqual(status.returncode, 0, streams)
         self.assertIn('OK', status.stderr)
-        self.assertTrue('FAIL' not in status.stderr)
-        self.assertTrue('ERROR' not in status.stderr)
+        self.assertNotIn('FAIL', status.stderr)
+        self.assertNotIn('ERROR', status.stderr)
 
 
 class SerialMixin(object):
 
@@ -7,6 +7,10 @@
 import unittest
 import llvmlite.binding as llvm
 
+#NOTE: These tests are potentially sensitive to changes in SSA or lowering
+# behaviour and may need updating should changes be made to the corresponding
+# algorithms.
+
 
 class TestDebugInfo(TestCase):
     """
@@ -295,14 +299,14 @@ def foo(a):
         sig = (types.float64[::1],)
         full_ir = self._get_llvmir(foo, sig=sig)
 
-        # make sure decref lines end with `meminfo.<number>)`.
+        # make sure decref lines end with `meminfo.<number>)` without !dbg info.
         count = 0
         for line in full_ir.splitlines():
             line_stripped = line.strip()
             if line_stripped.startswith('call void @NRT_decref'):
                 self.assertRegex(line, r'.*meminfo\.[0-9]+\)$')
                 count += 1
-        self.assertTrue(count > 0) # make sure there were some decrefs!
+        self.assertGreater(count, 0) # make sure there were some decrefs!
 
     def test_DILocation_decref(self):
         # Test runner for test_DILocation_decref_impl, needs a subprocess
 
@@ -43,7 +43,8 @@
 from numba.tests.support import (TestCase, captured_stdout, MemoryLeakMixin,
                       override_env_config, linux_only, tag,
                       skip_parfors_unsupported, _32bit, needs_blas,
-                      needs_lapack, disabled_test, skip_unless_scipy)
+                      needs_lapack, disabled_test, skip_unless_scipy,
+                      needs_subprocess)
 import cmath
 import unittest
 
@@ -52,9 +53,8 @@
 # used to determine whether a test is skipped or not, such that if you want to
 # run any parfors test directly this environment variable can be set. The
 # subprocesses running the test classes set this environment variable as the new
-# process starts which enables the tests within the process.
-_exec_cond = os.environ.get('SUBPROC_TEST', None) == '1'
-needs_subprocess = unittest.skipUnless(_exec_cond, "needs subprocess harness")
+# process starts which enables the tests within the process. The decorator
+# @needs_subprocess is used to ensure the appropriate test skips are made.
 
 
 @skip_parfors_unsupported