Mingyang Li made a great effort to explain the difference between these popular terms which I've often seen used exchangeably.
There are quite a few so-called "test shapes", such as test pyramids, that help describe testing strategy. Carolina Ramirez gives a brief overview of the most popular ones.
And since it's related to the test levels, Wessel Braakman wrote a good Introduction to Contract Testing.
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Wondering how Spotify load tests its Wrapped feature that summarises a year for millions of users? Well, here's Fred Wang explaining all that!