Commentary: git diff origin/develop -- reducers/authentication.test.js

1. initialState extracted as a constant.

Before: object was hardcoded in the test it('initial state') as { loading: false, error: null, loggedIn: false }.

After: the constant initialState, kfromwhich k matches c initialState from the reducer itself [reducers/authentication.js:3].

2. loading: false → loading: true.

Old init: loading: false — user not logged in, no spinner.

New init: loading: true — on app load, loadUserStatus() runs immediately to check the session. Initial state — 'looking for user'. This reducer change commit 8b3b44be7 (2020-03-18).

3. loggedIn: false → user: null. MAIN STATE SHAPE CHANGE.

• loggedIn: true after login → now user: { name: 'test', ... }
• loggedIn: false before login → now user: null
• Components check user !== null instead of loggedIn === true
• Corresponds to the migration connect() → useSelector [react-redux hooks]

unknown action → unknown action returns current state. Explicit description: 'reducer doesn't know this action → returns current state unchanged'. The old test didn't say what it was actually verifying.

Input state change: old test checked { loading: true, loggedIn: false }, new one — { loading: false, user: { name: 'test' } }. Chose a logged-in user state to verify that user is not nulled on unknown action — guarantee of a pure function [Redux reducers].

Formatting: old call split across 3 lines, new one — single line. Style only.

Object.freeze(state) [MDN] — mutation protection: if the reducer modifies the passed state (violating purity), the test will fail with an error.

describe('handles USER_LOGIN_BEGIN') → describe('USER_LOGIN_BEGIN'). Removed the word handles — in the new style, all describe blocks are named after the action literally. [new file]^⚡

2 of 3 tests deleted.

«fresh state» — verified transition from { loading: false, error: null, ... } → { loading: true, error: null, ... }. [line 34]

«error state» — verified transition from { loading: false, error: exampleError, ... } → { loading: true, error: null, ... }. [line 53]

Both tests verify the same thing: error is nulled, loading becomes true. The difference — in the original error (null vs line). Redundant — one test covers both cases.

«loggedIn state» — input: { loading: false, error: null, loggedIn: false } — completely matches 'fresh state'. Possibly a typo (should have been loggedIn: true). [line 72]

One new test: 'resets to loading with null user' [new file]^⚡

• Input: { loading: false, error: 'some error', user: { name: 'old' } }
• Output: { loading: true, error: null, user: null }
• Verifies that user is nulled (stricter than loggedIn: false — full reset)
• error is nulled, loading becomes true — as in the old tests
• Replaceto loggedIn: false to user: null — key state shape difference

Old test «loading state» — WITHOUT PAYLOAD.

Called { type: 'USER_LOGIN_SUCCESS' } without the third argument (payload). The old reducer supposedly just set loggedIn: true u loading: false — user data was not saved.

Deleted «weird state»: { loading: false, error: exampleError, loggedIn: true } — nonsensical combination: error present with loggedIn = true. [line 115]

New test — with actual payload:

Why these exact fields: the reducer at authentication.js:18-27 expects four payload fields — each written directly to state:

The old test passed no payload at all — so it verified none of these fields. The new test checks full correspondence.

loggedIn: true → user: { name: 'testuser' }. Components check state.user !== null instead of state.loggedIn === true — part of the migration to react-redux hooks.

Similar changes: handles USER_LOGIN_FAILURE → USER_LOGIN_FAILURE, 'weird state' deleted, one test instead of two.

New description: 'sets error and clears user/loading' — explicitly states what happens: error stored, user reset, spinner removed.

loggedIn: false → user: null. The user field becomes null on error. This is stricter than loggedIn: false — the old approach kept user data in state (just marked as not logged in), the new one fully clears it. Cofromesponds case USER_LOGIN_FAILURE: user: null.

Formatting payload: { error: exampleError } to one line instead of three. Style only.

Deleted entirely (2 tests, ~40 lines).

Verified that USER_LOGOUT resets { loggedIn: true } b { loggedIn: false } u nulls the error.

Why deleted:

1. Action USER_LOGOUT no longer exists — not exported from authentication.js (imports only USER_LOGIN_BEGIN, USER_LOGIN_FAILURE, USER_LOGIN_SUCCESS).
2. USER_LOGOUT not in the reducer switch [only 3 case].
3. Functotionality of logout covered by USER_LOGIN_BEGIN — both reset the state.
4. The test imported USER_LOGOUT from a nonexistent export — the test was broken.

Historically: USER_LOGOUT was removed from the source commit 7c60c2fbb (2019-07-13, «implemented logout check») — from actions/authentication.js and from the reducer. But the test was not updated — it continued importing and testing USER_LOGOUT for 7 more years. In the new reducer, logout is simply USER_LOGIN_BEGIN (reset to loading).

Redux reducer

Pure function: (state, action) → new state. No side effects, no mutations. Object.freeze(state) in the test guarantees this: if the reducer accidentally mutates the passed state, the test fails. [Redux docs]

State shape: loggedIn → user

Old state: { loading, error, loggedIn }. New: { loading, error, user }. loggedIn: boolean only said "yes/no". user: object|null provides the full user object (id, name, locale, ...) — components get all data at once via useSelector(state => state.authentication.user).

Object.freeze

Makes an object immutable. In the reducer test: Object.freeze(state); reducer(state, action); — if the reducer tries to mutate the state (instead of creating a new one), JavaScript throws an error in strict mode. This verifies function purity. [MDN]