# `Chronicle.Testing.UnsupportedProjectionOperation`
[🔗](https://github.com/Cratis/Chronicle.Elixir/blob/main/lib/chronicle/testing/unsupported_projection_operation.ex#L4)

Raised by `Chronicle.Testing.Projections` when a read model declares a
projection operation the in-memory evaluator does not support — `join/2`,
`children/2`, `from_every/1` and their variants.

These need the server-side projection engine; use
`Chronicle.Testing.Integration.setup_isolated_client/2` against a real kernel
instead of evaluating the projection in memory.

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*Consult [api-reference.md](api-reference.md) for complete listing*