[python] [tests] Remove cdb lookup failure test

[mgorny]

Summary

Remove the test checking for compilation db lookup failure.
Since r342228, JSONCompilationDatabasePlugin infers compile commands for
missing files, therefore making the lookup always succeed.

[sammccall]

We could verify the fuzzy-matched results, but we have pretty good testing on the C++ side, so a smoke test here seems fine.

[mgorny]

Thanks for the review!

bindings/python/tests/cindex/test_cdb.py

def test_create_fail(self):
         e = cm.exception
         self.assertEqual(e.cdb_error,
             CompilationDatabaseError.ERROR_CANNOTLOADDATABASE)
 
     def test_create(self):
         """Check we can load a compilation database"""
         cdb = CompilationDatabase.fromDirectory(kInputsDir)
 
-    def test_lookup_fail(self):
-        """Check file lookup failure"""
-        cdb = CompilationDatabase.fromDirectory(kInputsDir)
-        self.assertIsNone(cdb.getCompileCommands('file_do_not_exist.cpp'))
-
     def test_lookup_succeed(self):
         """Check we get some results if the file exists in the db"""
         cdb = CompilationDatabase.fromDirectory(kInputsDir)
         cmds = cdb.getCompileCommands('/home/john.doe/MyProject/project.cpp')
         self.assertNotEqual(len(cmds), 0)
 
     def test_all_compilecommand(self):
         """Check we get all results from the db"""