When should you use test snapshots?

At Woovi we have more than 6000 tests. Constantly comes the doubt if we must use snapshots or not.

What is a snapshot?

Snapshot is a way of storing the expected return to guarantee that the return has always been the same.

When can you use a snapshot?

Let's imagine that we have an API, and we need all the fields to be defined, instead of doing this next:

expect(response.body.value).toBeDefined();
expect(response.body.expiresIn).toBeDefined();
expect(response.body.correlationID).toBeDefined();
...

We can use a snapshot in response.body, guaranteeing that all fields will be defined.

expect(response.body).toMatchSnapshot();

exports[`should return 3 fields 1`] = `
{
  "value": 1000,
  "expiresIn": 2592000,
  "correlationID": "correlationID",
}
`;

When can't you use a snapshot?

We saw that snapshots are good for verifying many fields, but otherwise, they are bad when you want to test a specific field.

For example, we need to verify if only 1 field is defined, instead of taking a snapshot, we can verify this field directly, like this:

expect(request.body.expiresDate).toBeDefined();

Taking snapshots for these cases makes testing confusing because you don't know the fields you are testing.

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