diff --git a/lib/assert.js b/lib/assert.js
index 15818739c..a55a06721 100644
--- a/lib/assert.js
+++ b/lib/assert.js
@@ -27,7 +27,7 @@ function formatWithLabel(label, value) {
 	return formatDescriptorWithLabel(label, concordance.describe(value, concordanceOptions));
 }
 
-const hasOwnProperty = (object, prop) => Object.prototype.hasOwnProperty.call(object, prop);
+export const hasOwnProperty = (object, prop) => Object.prototype.hasOwnProperty.call(object, prop);
 const noop = () => {};
 const notImplemented = () => {
 	throw new Error('not implemented');
diff --git a/lib/test.js b/lib/test.js
index 816b7dda2..6f7827bb2 100644
--- a/lib/test.js
+++ b/lib/test.js
@@ -2,7 +2,7 @@ import concordance from 'concordance';
 import isPromise from 'is-promise';
 import plur from 'plur';
 
-import {AssertionError, Assertions, checkAssertionMessage} from './assert.js';
+import {AssertionError, Assertions, checkAssertionMessage, hasOwnProperty} from './assert.js';
 import concordanceOptions from './concordance-options.js';
 import nowAndTimers from './now-and-timers.cjs';
 import parseTestArgs from './parse-test-args.js';
@@ -14,7 +14,7 @@ function isExternalAssertError(error) {
 	}
 
 	// Match errors thrown by <https://www.npmjs.com/package/chai> and <https://nodejs.org/api/assert.html>.
-	return error.hasOwnProperty('actual') && error.hasOwnProperty('expected');
+	return hasOwnProperty(error, 'actual') && hasOwnProperty(error, 'expected');
 }
 
 function formatErrorValue(label, error) {
@@ -533,13 +533,13 @@ export default class Test {
 				this.saveFirstError(new AssertionError({
 					message: 'Assertion failed',
 					savedError: result.error instanceof Error && result.error,
-					values: [{label: 'Assertion failed: ', formatted: result.error.message}]
+					values: [{label: 'Assertion failed: ', formatted: result.error.message}],
 				}));
 			} else {
 				this.saveFirstError(new AssertionError({
 					message: 'Error thrown in test',
 					savedError: result.error instanceof Error && result.error,
-					values: [formatErrorValue('Error thrown in test:', result.error)]
+					values: [formatErrorValue('Error thrown in test:', result.error)],
 				}));
 			}
 
@@ -586,13 +586,13 @@ export default class Test {
 							this.saveFirstError(new AssertionError({
 								message: 'Assertion failed',
 								savedError: error instanceof Error && error,
-								values: [{label: 'Assertion failed: ', formatted: error.message}]
+								values: [{label: 'Assertion failed: ', formatted: error.message}],
 							}));
 						} else {
 							this.saveFirstError(new AssertionError({
 								message: 'Rejected promise returned by test',
 								savedError: error instanceof Error && error,
-								values: [formatErrorValue('Rejected promise returned by test. Reason:', error)]
+								values: [formatErrorValue('Rejected promise returned by test. Reason:', error)],
 							}));
 						}
 					})
diff --git a/test/external-assertions/fixtures/expect-failure.js b/test/external-assertions/fixtures/expect-failure.js
index 2825f9cad..b410bc858 100644
--- a/test/external-assertions/fixtures/expect-failure.js
+++ b/test/external-assertions/fixtures/expect-failure.js
@@ -1,6 +1,5 @@
-import { expect } from 'expect';
-
 import test from 'ava';
+import {expect} from 'expect';
 
 test('test', () => {
 	expect(false).toBeTruthy();