--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -1074,16 +1074,21 @@ class TreeMetadataEmitter(LoggingMixin):
                 for obj in self._process_reftest_manifest(context, flavor, path, manifest):
                     yield obj
 
         for flavor in WEB_PATFORM_TESTS_FLAVORS:
             for path, manifest in context.get("%s_MANIFESTS" % flavor.upper().replace('-', '_'), []):
                 for obj in self._process_web_platform_tests_manifest(context, path, manifest):
                     yield obj
 
+        python_tests = context.get('PYTHON_UNIT_TESTS')
+        if python_tests:
+            for obj in self._process_python_tests(context, python_tests):
+                yield obj
+
     def _process_test_manifest(self, context, info, manifest_path, mpmanifest):
         flavor, install_root, install_subdir, package_tests = info
 
         path = mozpath.normpath(mozpath.join(context.srcdir, manifest_path))
         manifest_dir = mozpath.dirname(path)
         manifest_reldir = mozpath.dirname(mozpath.relpath(path,
             context.config.topsrcdir))
         install_prefix = mozpath.join(install_root, install_subdir)
@@ -1277,16 +1282,46 @@ class TreeMetadataEmitter(LoggingMixin):
                     'head': '',
                     'tail': '',
                     'support-files': '',
                     'subsuite': '',
                 })
 
         yield obj
 
+    def _process_python_tests(self, context, python_tests):
+        manifest_full_path = context.main_path
+        manifest_reldir = mozpath.dirname(mozpath.relpath(manifest_full_path,
+            context.config.topsrcdir))
+
+        obj = TestManifest(context, manifest_full_path,
+                mozpath.basename(manifest_full_path),
+                flavor='python', install_prefix='python/',
+                relpath=mozpath.join(manifest_reldir,
+                    mozpath.basename(manifest_full_path)))
+
+        for test in python_tests:
+            test = mozpath.normpath(mozpath.join(context.srcdir, test))
+            if not os.path.isfile(test):
+                raise SandboxValidationError('Path specified in '
+                   'PYTHON_UNIT_TESTS does not exist: %s' % test,
+                   context)
+            obj.tests.append({
+                'path': test,
+                'here': mozpath.dirname(test),
+                'manifest': manifest_full_path,
+                'name': mozpath.basename(test),
+                'head': '',
+                'tail': '',
+                'support-files': '',
+                'subsuite': '',
+            })
+
+        yield obj
+
     def _process_jar_manifests(self, context):
         jar_manifests = context.get('JAR_MANIFESTS', [])
         if len(jar_manifests) > 1:
             raise SandboxValidationError('While JAR_MANIFESTS is a list, '
                 'it is currently limited to one value.', context)
 
         for path in jar_manifests:
             yield JARManifest(context, path)

--- a/python/mozbuild/mozbuild/test/frontend/data/test-manifest-keys-extracted/moz.build
+++ b/python/mozbuild/mozbuild/test/frontend/data/test-manifest-keys-extracted/moz.build
@@ -4,8 +4,9 @@
 A11Y_MANIFESTS += ['a11y.ini']
 BROWSER_CHROME_MANIFESTS += ['browser.ini']
 METRO_CHROME_MANIFESTS += ['metro.ini']
 MOCHITEST_MANIFESTS += ['mochitest.ini']
 MOCHITEST_CHROME_MANIFESTS += ['chrome.ini']
 XPCSHELL_TESTS_MANIFESTS += ['xpcshell.ini']
 REFTEST_MANIFESTS += ['reftest.list']
 CRASHTEST_MANIFESTS += ['crashtest.list']
+PYTHON_UNIT_TESTS += ['test_foo.py']

new file mode 100644

new file mode 100644
--- /dev/null
+++ b/python/mozbuild/mozbuild/test/frontend/data/test-python-unit-test-missing/moz.build
@@ -0,0 +1,4 @@
+# Any copyright is dedicated to the Public Domain.
+# http://creativecommons.org/publicdomain/zero/1.0/
+
+PYTHON_UNIT_TESTS += ['test_foo.py']

--- a/python/mozbuild/mozbuild/test/frontend/test_emitter.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
@@ -475,25 +475,31 @@ class TestEmitterBasic(unittest.TestCase
             'reftest1-ref.html': 'reftest.list',
             'reftest2.html': 'included-reftest.list',
             'reftest2-ref.html': 'included-reftest.list',
         }
 
         for t in obj.tests:
             self.assertTrue(t['manifest'].endswith(expected_manifests[t['name']]))
 
+    def test_python_unit_test_missing(self):
+        """Missing files in PYTHON_UNIT_TESTS should raise."""
+        reader = self.reader('test-python-unit-test-missing')
+        with self.assertRaisesRegexp(SandboxValidationError,
+            'Path specified in PYTHON_UNIT_TESTS does not exist:'):
+            objs = self.read_topsrcdir(reader)
 
     def test_test_manifest_keys_extracted(self):
         """Ensure all metadata from test manifests is extracted."""
         reader = self.reader('test-manifest-keys-extracted')
 
         objs = [o for o in self.read_topsrcdir(reader)
                 if isinstance(o, TestManifest)]
 
-        self.assertEqual(len(objs), 8)
+        self.assertEqual(len(objs), 9)
 
         metadata = {
             'a11y.ini': {
                 'flavor': 'a11y',
                 'installs': {
                     'a11y.ini': False,
                     'test_a11y.js': True,
                 },
@@ -548,16 +554,20 @@ class TestEmitterBasic(unittest.TestCase
             'reftest.list': {
                 'flavor': 'reftest',
                 'installs': {},
             },
             'crashtest.list': {
                 'flavor': 'crashtest',
                 'installs': {},
             },
+            'moz.build': {
+                'flavor': 'python',
+                'installs': {},
+            }
         }
 
         for o in objs:
             m = metadata[mozpath.basename(o.manifest_relpath)]
 
             self.assertTrue(o.path.startswith(o.directory))
             self.assertEqual(o.flavor, m['flavor'])
             self.assertEqual(o.dupe_manifest, m.get('dupe', False))

--- a/python/mozbuild/mozbuild/testing.py
+++ b/python/mozbuild/mozbuild/testing.py
@@ -279,17 +279,18 @@ TEST_MANIFESTS = dict(
 REFTEST_FLAVORS = ('crashtest', 'reftest')
 
 # Web platform tests have their own manifest format and are processed separately.
 WEB_PATFORM_TESTS_FLAVORS = ('web-platform-tests',)
 
 def all_test_flavors():
     return ([v[0] for v in TEST_MANIFESTS.values()] +
             list(REFTEST_FLAVORS) +
-            list(WEB_PATFORM_TESTS_FLAVORS))
+            list(WEB_PATFORM_TESTS_FLAVORS) +
+            ['python'])
 
 # Convenience methods for test manifest reading.
 def read_manifestparser_manifest(context, manifest_path):
     path = mozpath.normpath(mozpath.join(context.srcdir, manifest_path))
     return manifestparser.TestManifest(manifests=[path], strict=True,
                                        rootdir=context.config.topsrcdir,
                                        finder=context._finder)