Add more router unittests

[darenliang]

Until recently, there are only basic tests for helper functions in the query folder.

Now, the newly created router folder has its own unittests.

These tests are meant to be more robust and should test in a more "practical" setting, by running the actual API server and verifying responses.

There's only one test for now, adding more tests will definitely be helpful in catching errors, bugs, breaking changes, etc.

[darenliang]

Closing this issue because there are a few more unittests added.