List of non-essential tests.

[jiaqima]

This issue maintains a list of tests that are non-essential in the sense that an error here will lead to an error in a more high-level test (e.g., test of get_glb_dataset), so the error will still be catched without these tests. But the existence of these more low-level tests could enhance the user experience for debugging contributed datasets.

• [ ] Add a test ensuring that there is no unexpected attribute in metadata.json and task.json. May need to maintain a list of predefined attributes that are allowed.
• [ ] Test the validity of json file formats.
  • [ ] No trailing comma after the last entry value within each pair of curly braces.
  • [ ] The json file can be successfully loaded.