chai

Postconditions — what we check

• expect · expect-assertion-failure

  warning
  Whenassertion fails (e.g., expect(value).to.equal(expected) when value !== expected)
  ThrowsAssertionError
  Required handlingAssertions are EXPECTED to throw in test code, but if used outside tests (e.g., in production validation), callers MUST wrap in try-catch. Without error handling, failed assertions crash the application. Use pattern: try { expect(value).to.equal(expected); } catch (error) { /* handle */ }
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[1]
• assert · assert-assertion-failure

  warning
  Whenassertion fails (e.g., assert.equal(actual, expected) when actual !== expected)
  ThrowsAssertionError
  Required handlingAssert-style assertions throw AssertionError on failure. In test code, this is expected. If used in production code, MUST wrap in try-catch to prevent crashes.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[2]
• should · should-assertion-failure

  warning
  Whenassertion fails (e.g., value.should.equal(expected) when value !== expected)
  ThrowsAssertionError
  Required handlingShould-style assertions throw AssertionError on failure. Primarily for test code. If used outside tests, MUST wrap in try-catch.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[1]
• assert.ifError · assert-iferror-rethrows-value

  warning
  Whenval is truthy (non-null, non-undefined, non-zero, non-false, non-empty-string). Common usage: assert.ifError(err) in callback-style code where err is an Error. Throws val directly — NOT wrapped in AssertionError.
  Throwsval (the original value passed — typically an Error, but any truthy value)
  Required handlingWhen assert.ifError(err) is used in production code (not test code), the caller must catch the rethrown error with the correct type. A catch block that expects AssertionError will NOT catch errors from assert.ifError — it rethrows the original value as-is. Correct pattern for production use: try { assert.ifError(err); // rethrows err if err is truthy } catch (e) { // e is err itself, not an AssertionError console.error('Callback error:', e.message); throw e; } Note: In test code, assert.ifError is typically called at the top of a callback to fail the test immediately if err is present. The rethrow causes test frameworks to mark the test as failed.
  costmediumin prodsilent failureusers seeservice unavailablevisibilitysilent
  Sources[3][2]

Sources

Every postcondition cites at least one of these. Numbered to match the footnotes above.

1. [1]chaijs.com/api/bddhttps://www.chaijs.com/api/bdd/
2. [2]chaijs.com/api/asserthttps://www.chaijs.com/api/assert/
3. [3]chaijs.com/api/asserthttps://www.chaijs.com/api/assert/#method_iferror