readme draft

x-pack/plugins/security_solution/public/resolver/mocks/README.md

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+* reuse in mocks is good
+  - because if all mocks need to change, you change them easier and have all the tests run against the new version?
+    - if theres a bug in the way we make a mock, we want to fix it everywhere
+    - the mock mocks something we have in production, so if the iterface or design that changes, all mocks need to change
+* mocks should have deterministic, concrete, unique, interesting behavior:
+  - a resolver tree with no ancestors
+    - 2 children
+    - the origin has 2 related events
+  - 'when analyzing a tree with 2 children'
+  - 'when analyzing a tree with no ancestors'
+
+* internally to the 'mocks' module
+  - feel free to use helpers, composition, configuration, parameters, etc
+
+* mocks exported should have little or no configuration, a very specific name,
+
+* mock metadata
+  - when a mock uses interesting data like entity_ids, process names, times, PIDs, etc, that a test will check, then export that stuff in an object from the module that defines the mock
+    - that way it can be used in the `describe` and `it` blocks that give the test a name
+
+* prefer to mock DataAccessLayer and ResolverTree
+  - also mock the payloads of any action