wip: code formatting nits continued

test/isError.spec.js

@@ -0,0 +1,64 @@
+import lodashStable from 'lodash';
+
+import {
+    errors,
+    stubTrue,
+    CustomError,
+    falsey,
+    stubFalse,
+    args,
+    slice,
+    symbol,
+    realm,
+} from './utils';
+
+import isError from '../src/isError';
+
+describe('isError', () => {
+    it('should return `true` for error objects', () => {
+        const expected = lodashStable.map(errors, stubTrue);
+
+        const actual = lodashStable.map(errors, (error) => isError(error) === true);
+
+        expect(actual).toEqual(expected);
+    });
+
+    it('should return `true` for subclassed values', () => {
+        expect(isError(new CustomError('x'))).toBe(true);
+    });
+
+    it('should return `false` for non error objects', () => {
+        const expected = lodashStable.map(falsey, stubFalse);
+
+        const actual = lodashStable.map(falsey, (value, index) =>
+            index ? isError(value) : isError(),
+        );
+
+        expect(actual).toEqual(expected);
+
+        expect(isError(args)).toBe(false);
+        expect(isError([1, 2, 3])).toBe(false);
+        expect(isError(true)).toBe(false);
+        expect(isError(new Date())).toBe(false);
+        expect(isError(slice)).toBe(false);
+        expect(isError({ a: 1 })).toBe(false);
+        expect(isError(1)).toBe(false);
+        expect(isError(/x/)).toBe(false);
+        expect(isError('a')).toBe(false);
+        expect(isError(symbol)).toBe(false);
+    });
+
+    it('should return `false` for plain objects', () => {
+        expect(isError({ name: 'Error', message: '' })).toBe(false);
+    });
+
+    it('should work with an error object from another realm', () => {
+        if (realm.errors) {
+            const expected = lodashStable.map(realm.errors, stubTrue);
+
+            const actual = lodashStable.map(realm.errors, (error) => isError(error) === true);
+
+            expect(actual).toEqual(expected);
+        }
+    });
+});