Asserting a dictionary is a subset of another dictionary

My lazy approach to writing unit tests means that sometimes I want to run an assertion against most (but not all) of a dictionary.

Take for example an API endpoint that returns something like this:

{
    "sqlite_version": "3.27.1",
    "name": "Datasette",
    "columns": ["foo", "bar"]
}

I want to efficiently assert against the second two keys, but I don't want to hard-code the SQLite version into my test in case it changes in the future.

Solution:

assert {
    "name": "Datasette",
    "columns": ["foo", "bar"]
}.items() <= api_response.items()

The trick here is using expected.items() <= actual.items() to assert that one dictionary is a subset of another.

Here's a recent example test that uses this trick: https://github.com/simonw/datasette/blob/40885ef24e32d91502b6b8bbad1c7376f50f2830/tests/test_plugins.py#L414-L446

Created 2020-05-28T08:09:14-07:00 · Edit

Asserting a dictionary is a subset of another dictionary

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