Glossary

[nedtwigg]

• Subject - a single value (string or binary) which best records a snapshotted entity
• Facet - a single named value (string or binary) which records a single aspect or point of view of a snapshotted entity
• Snapshot - a combination of a subject and zero or more facets which captures all relevant data of an entity whose behavior we wish to record and specify
• Camera - a function that transforms a specific type of entity into a snapshot
• Lens - a function which transforms one snapshot into a new snapshot, usually by adding new facets that emphasize a certain point of view of the subject, but possibly also by cleaning the existing subject and facets
• Equality assertion - a success condition which requires a value under to test to exactly match an expected value
• Inline snapshot - an equality assertion where the expected value can be written into the sourcecode by automated tooling
• Inline literal snapshot - an inline snapshot where the expected value must always be a source code literal, never a compound expression
  • expect(2 + 2).toMatchInlineSnapshot(4) <-- inline literal snapshot
  • expect(2 + 2).toMatchInlineSnapshot(2 * 2) <-- inline literal snapshot, because it's not literal, when tooling modifies the value inside (), it can't do a self-error-check to make sure it has correctly parsed the same value which got passed at runtime
  • Conversationally people will say "inline snapshot", "literal snapshot", "inline literal snapshot", etc. They mostly mean the same thing, but in selfie we will try to always say "inline literal".

If you think any of these terms are unclear, feel free to discuss below. If there are any other concepts in the code which should be defined explicitly, feel free to discuss below. The final result of all discussions is incorporated into the list above via editing, after which the discussions may be deleted. This glossary is based on an idea from Rich Hickey's Design in Practice talk.