id: no-self-comparison-assertion
language: Tsx
severity: error
message: 'This compares an expression against itself (e.g. expect(result.id).toBe(result.id)). ast-grep metavariables enforce identical text, so both sides read the same value the same way; nearly every real occurrence of this shape is a copy-paste bug where the second operand should have been an independently derived expected value. Compare against that instead, or a fixture-provided value the code under test did not produce. (Two syntactic shapes are exempted because they cannot be tautological by construction: an expression containing a call anywhere in it, e.g. expect(f(a)).toBe(f(a)) or expect((await load()).id).toBe((await load()).id), is a fresh invocation on each side and legitimately tests that the call is deterministic/pure; and a postfix/prefix increment or decrement, e.g. expect(index++).toBe(index++), advances state between the two reads. A getter or other stateful property access is NOT exempted -- ast-grep cannot see whether a given `.foo` is a plain field or a getter with side effects, and every real violation this rule has caught in this repo is a plain field, so this stays flagged by design; if you are deliberately asserting that such an accessor is stable across two reads, add an `ast-grep-ignore: no-self-comparison-assertion` comment with that rationale instead of weakening this rule.)'
files:
  - '**/*.test.ts'
  - '**/*.test.mts'
  - '**/*.test.cts'
  - '**/*.spec.ts'
  - '**/*.spec.mts'
  - '**/*.spec.cts'
  - '**/*.test.tsx'
  - '**/*.spec.tsx'
rule:
  pattern: 'expect($X).toBe($X)'
constraints:
  X:
    not:
      any:
        - kind: 'true'
        - kind: 'false'
        - kind: 'number'
        - kind: 'string'
        - kind: 'null'
        - kind: 'undefined'
        - kind: 'call_expression'
        - kind: 'update_expression'
        - has:
            kind: 'call_expression'
            stopBy: end
examples:
  - code: 'expect(result.id).toBe(result.id)'
    isValid: false
    file: 'backend/services/example/__tests__/items.test.mts'
  - code: 'expect(conversationId).toBe(conversationId)'
    isValid: false
    file: 'src/__tests__/routes.user-admin.part-5.test.mts'
  - code: 'expect(result.id).toBe(expectedId)'
    isValid: true
    file: 'backend/services/example/__tests__/items.test.mts'
  - code: 'expect(await run()).not.toBeNull()'
    isValid: true
    file: 'src/__tests__/routes.user-admin.part-5.test.mts'
  - code: 'expect(buildCanonicalRequestString(...args)).toBe(buildCanonicalRequestString(...args))'
    isValid: true
    file: 'backend/services/example/request-canonical.test.mts'
  - code: 'expect((await load()).id).toBe((await load()).id)'
    isValid: true
    file: 'backend/services/example/__tests__/items.test.mts'
  - code: 'expect(result.id).toBe(result.id)'
    isValid: true
    file: 'backend/services/example/items.mts'
  - code: 'expect(index++).toBe(index++)'
    isValid: true
    file: 'backend/services/example/__tests__/items.test.mts'
  - code: expect(item.id).toBe(item.id)
    isValid: false
    file: web/components/example/__tests__/add-to-list-menu-item.mock.test.tsx
  - code: expect(item.id).toBe(expectedId)
    isValid: true
    file: web/components/example/__tests__/add-to-list-menu-item.mock.test.tsx
  - code: expect(formatItemLabel(item)).toBe(formatItemLabel(item))
    isValid: true
    file: web/components/example/__tests__/add-to-list-menu-item.mock.test.tsx
  - code: expect((await loadItem()).id).toBe((await loadItem()).id)
    isValid: true
    file: web/components/example/__tests__/add-to-list-menu-item.mock.test.tsx
  - code: expect(item.id).toBe(item.id)
    isValid: true
    file: web/components/example/add-to-list-menu-item.tsx
  - code: expect(index++).toBe(index++)
    isValid: true
    file: web/components/example/__tests__/add-to-list-menu-item.mock.test.tsx