tests: Iterate files using os.path

We cannot always rely on git to iterate through the files

Signed-off-by: Kapileshwar Singh <kapileshwar.singh@arm.com>
diff --git a/tests/test_copyright.py b/tests/test_copyright.py
index 619fb99..b123fd1 100644
--- a/tests/test_copyright.py
+++ b/tests/test_copyright.py
@@ -56,11 +56,15 @@
 class TestCopyRight(unittest.TestCase):
     def test_copyrights(self):
         """Check that all files have valid copyrights"""
-        files_in_repo = subprocess.check_output(["git", "ls-files"])
 
-        for fname in files_in_repo.split():
-            extension = os.path.splitext(fname)[1]
-            if extension in [".py", ".js", ".css"]:
-                if not copyright_is_valid(fname):
-                    print("Invalid copyright in {}".format(fname))
-                    self.fail()
+        tests_dir = os.path.dirname(os.path.abspath(__file__))
+        base_dir = os.path.dirname(tests_dir)
+
+        for root, _, files in os.walk(base_dir):
+            for fname in files:
+                fname = os.path.join(root, fname)
+                extension = os.path.splitext(fname)[1]
+                if extension in [".py", ".js", ".css"]:
+                    if not copyright_is_valid(fname):
+                        print("Invalid copyright in {}".format(fname))
+                        self.fail()