fix(expect)!: check more properties for error equality (#5876)

Co-authored-by: Vladimir <[email protected]>

Author: hi-ogawa

docs/api/expect.md

@@ -431,7 +431,17 @@ test('stocks are not the same', () => {
 ```
 
 :::warning
-A _deep equality_ will not be performed for `Error` objects. Only the `message` property of an Error is considered for equality. To customize equality to check properties other than `message`, use [`expect.addEqualityTesters`](#expect-addequalitytesters). To test if something was thrown, use [`toThrowError`](#tothrowerror) assertion.
+For `Error` objects, non-enumerable properties such as `name`, `message`, `cause` and `AggregateError.errors` are also compared. For `Error.cause`, the comparison is done asymmetrically:
+
+```ts
+// success
+expect(new Error('hi', { cause: 'x' })).toEqual(new Error('hi'))
+
+// fail
+expect(new Error('hi')).toEqual(new Error('hi', { cause: 'x' }))
+```
+
+To test if something was thrown, use [`toThrowError`](#tothrowerror) assertion.
 :::
 
 ## toStrictEqual
@@ -649,8 +659,9 @@ test('the number of elements must match exactly', () => {
 
 You can provide an optional argument to test that a specific error is thrown:
 
-- regular expression: error message matches the pattern
-- string: error message includes the substring
+- `RegExp`: error message matches the pattern
+- `string`: error message includes the substring
+- `Error`, `AsymmetricMatcher`: compare with a received object similar to `toEqual(received)`
 
 :::tip
 You must wrap the code in a function, otherwise the error will not be caught, and test will fail.
@@ -678,6 +689,13 @@ test('throws on pineapples', () => {
   expect(() => getFruitStock('pineapples')).toThrowError(
     /^Pineapples are not in stock$/,
   )
+
+  expect(() => getFruitStock('pineapples')).toThrowError(
+    new Error('Pineapples are not in stock'),
+  )
+  expect(() => getFruitStock('pineapples')).toThrowError(expect.objectContaining({
+    message: 'Pineapples are not in stock',
+  }))
 })
 ```
 

packages/expect/src/jest-expect.ts

@@ -794,12 +794,16 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
       }
 
       if (expected instanceof Error) {
+        const equal = jestEquals(thrown, expected, [
+          ...customTesters,
+          iterableEquality,
+        ])
         return this.assert(
-          thrown && expected.message === thrown.message,
-          `expected error to have message: ${expected.message}`,
-          `expected error not to have message: ${expected.message}`,
-          expected.message,
-          thrown && thrown.message,
+          equal,
+          'expected a thrown error to be #{exp}',
+          'expected a thrown error not to be #{exp}',
+          expected,
+          thrown,
         )
       }
 

packages/expect/src/jest-utils.ts

@@ -114,10 +114,6 @@ function eq(
     }
   }
 
-  if (a instanceof Error && b instanceof Error) {
-    return a.message === b.message
-  }
-
   if (typeof URL === 'function' && a instanceof URL && b instanceof URL) {
     return a.href === b.href
   }
@@ -196,6 +192,16 @@ function eq(
     return false
   }
 
+  if (a instanceof Error && b instanceof Error) {
+    try {
+      return isErrorEqual(a, b, aStack, bStack, customTesters, hasKey)
+    }
+    finally {
+      aStack.pop()
+      bStack.pop()
+    }
+  }
+
   // Deep compare objects.
   const aKeys = keys(a, hasKey)
   let key
@@ -225,6 +231,37 @@ function eq(
   return result
 }
 
+function isErrorEqual(
+  a: Error,
+  b: Error,
+  aStack: Array<unknown>,
+  bStack: Array<unknown>,
+  customTesters: Array<Tester>,
+  hasKey: any,
+) {
+  // https://nodejs.org/docs/latest-v22.x/api/assert.html#comparison-details
+  // - [[Prototype]] of objects are compared using the === operator.
+  // - Only enumerable "own" properties are considered.
+  // - Error names, messages, causes, and errors are always compared, even if these are not enumerable properties. errors is also compared.
+
+  let result = (
+    Object.getPrototypeOf(a) === Object.getPrototypeOf(b)
+    && a.name === b.name
+    && a.message === b.message
+  )
+  // check Error.cause asymmetrically
+  if (typeof b.cause !== 'undefined') {
+    result &&= eq(a.cause, b.cause, aStack, bStack, customTesters, hasKey)
+  }
+  // AggregateError.errors
+  if (a instanceof AggregateError && b instanceof AggregateError) {
+    result &&= eq(a.errors, b.errors, aStack, bStack, customTesters, hasKey)
+  }
+  // spread to compare enumerable properties
+  result &&= eq({ ...a }, { ...b }, aStack, bStack, customTesters, hasKey)
+  return result
+}
+
 function keys(obj: object, hasKey: (obj: object, key: string) => boolean) {
   const keys = []
 

packages/pretty-format/src/index.ts

@@ -296,6 +296,35 @@ function printComplexValue(
     )}}`
 }
 
+const ErrorPlugin: NewPlugin = {
+  test: val => val && val instanceof Error,
+  serialize(val: Error, config, indentation, depth, refs, printer) {
+    if (refs.includes(val)) {
+      return '[Circular]'
+    }
+    refs = [...refs, val]
+    const hitMaxDepth = ++depth > config.maxDepth
+    const { message, cause, ...rest } = val
+    const entries = {
+      message,
+      ...typeof cause !== 'undefined' ? { cause } : {},
+      ...val instanceof AggregateError ? { errors: val.errors } : {},
+      ...rest,
+    }
+    const name = val.name !== 'Error' ? val.name : getConstructorName(val as any)
+    return hitMaxDepth
+      ? `[${name}]`
+      : `${name} {${printIteratorEntries(
+        Object.entries(entries).values(),
+        config,
+        indentation,
+        depth,
+        refs,
+        printer,
+      )}}`
+  },
+}
+
 function isNewPlugin(plugin: Plugin): plugin is NewPlugin {
   return (plugin as NewPlugin).serialize != null
 }
@@ -535,11 +564,13 @@ export const plugins: {
   Immutable: NewPlugin
   ReactElement: NewPlugin
   ReactTestComponent: NewPlugin
+  Error: NewPlugin
 } = {
   AsymmetricMatcher,
   DOMCollection,
   DOMElement,
   Immutable,
   ReactElement,
   ReactTestComponent,
+  Error: ErrorPlugin,
 }

packages/utils/src/diff/index.ts

@@ -50,6 +50,7 @@ const PLUGINS = [
   DOMCollection,
   Immutable,
   AsymmetricMatcher,
+  prettyFormatPlugins.Error,
 ]
 const FORMAT_OPTIONS = {
   plugins: PLUGINS,
@@ -298,6 +299,19 @@ export function replaceAsymmetricMatcher(
     replacedActual: any
     replacedExpected: any
   } {
+  // handle asymmetric Error.cause diff
+  if (
+    actual instanceof Error
+    && expected instanceof Error
+    && typeof actual.cause !== 'undefined'
+    && typeof expected.cause === 'undefined'
+  ) {
+    delete actual.cause
+    return {
+      replacedActual: actual,
+      replacedExpected: expected,
+    }
+  }
   if (!isReplaceable(actual, expected)) {
     return { replacedActual: actual, replacedExpected: expected }
   }