Acting as a user

An action receives its caller, the person or service signed in, as a typed parameter (The principal). So a test passes one in:

test "bob cannot complete alice's todo" {    var alice: Principal.user = alice_with_todos()    var bob: Principal.user = bob_with_no_todos()    var todo: Todo = first_todo(alice)    assert complete_todo(todo.id, bob) fails TodoNotFound}

Here Bob tries to complete one of Alice's todos. Policy reports a record the caller may not see as the same not-found failure as a record that doesn't exist (Concealing records), so the test checks exactly what Bob would see.

Making a caller

Tests, fixtures and seeds make a user caller with Principal.user(user), and a service caller with Principal.service(service). Application code can't, because there a caller only comes from signing in.

Signing in for a route test

A route test signs in with as:, which goes through the application's real authentication. A service signs in with a key from Service.issue_key. So a disabled user is refused exactly as in production, and the sign-in checks are tested too.

Calls with no caller

A call a test, fixture or seed makes runs as the caller it passes, as complete_todo runs as Bob here. A call that passes none, such as one setting up data, runs without policy. So a call with no caller proves behaviour and data, and a route test or a call with a caller proves policy.