InFile.load_from_files should try to load only '.in' files

Source/build/scripts/in_file_unittest.py

Index: Source/build/scripts/in_file_unittest.py
diff --git a/Source/build/scripts/in_file_unittest.py b/Source/build/scripts/in_file_unittest.py
index e065d442987150afe98b0910ff3a814f53e5fbae..5b9d190903ca15ff7ccfcc6b4f8a55d0a83a13a5 100755
--- a/Source/build/scripts/in_file_unittest.py
+++ b/Source/build/scripts/in_file_unittest.py
@@ -72,6 +72,17 @@ name2
         }
         self.assertEquals(in_file.parameters, expected_parameters)
 
+    def test_assertion_for_non_in_files(self):
+        in_files = ['some_sample_file.json']
+        assertion_thrown = False
+        try:
+            in_file = InFile.load_from_files(in_files, None, None, None)
+        except AssertionError:
+            assertion_thrown = True
+        except:
+            pass
+        self.assertTrue(assertion_thrown)
+
 
 if __name__ == "__main__":
     unittest.main()