Fix issues with the isString helper

addon/-private/utils/is-string.js

@@ -1,3 +1,3 @@
-export default function isString() {
+export default function isString(object) {
   return typeof object === 'string';
 }

addon/mixins/legacy/normalize-error-response.js

@@ -79,23 +79,21 @@ export default Mixin.create({
           };
         }
       });
+    } else if (isString(payload)) {
+      return [
+        {
+          status: `${status}`,
+          title: payload
+        }
+      ];
     } else {
-      if (isString(payload)) {
-        return [
-          {
-            status: `${status}`,
-            title: payload
-          }
-        ];
-      } else {
-        return [
-          {
-            status: `${status}`,
-            title: payload.title || 'The backend responded with an error',
-            detail: payload
-          }
-        ];
-      }
+      return [
+        {
+          status: `${status}`,
+          title: payload.title || 'The backend responded with an error',
+          detail: payload
+        }
+      ];
     }
   }
 });

tests/unit/-private/promise-test.js

@@ -1,4 +1,4 @@
-import { describe, it, beforeEach } from 'mocha';
+import { describe, it } from 'mocha';
 import { expect } from 'chai';
 
 import AJAXPromise from 'ember-ajax/-private/promise';

tests/unit/-private/utils/is-string-test.js

@@ -0,0 +1,23 @@
+import { describe, it } from 'mocha';
+import { expect } from 'chai';
+import isString from 'ember-ajax/-private/utils/is-string';
+
+describe('-private/utils/is-string', function() {
+  it('detects when something is a string', function() {
+    expect(isString('foo')).to.be.ok;
+  });
+
+  describe('detecting something is not a string', function() {
+    it('handles a number', function() {
+      expect(isString(3)).not.to.be.ok;
+    });
+
+    it('handles `null`', function() {
+      expect(isString(null)).not.to.be.ok;
+    });
+
+    it('handles `undefined`', function() {
+      expect(isString(undefined)).not.to.be.ok;
+    });
+  });
+});

tests/unit/mixins/legacy/normalize-error-response-test.js

@@ -5,11 +5,10 @@ import LegacyNormalizeErrorResponseMixin from 'ember-ajax/mixins/legacy/normaliz
 
 const { Object: EmberObject } = Ember;
 const AjaxRequest = EmberObject.extend(LegacyNormalizeErrorResponseMixin);
+const service = new AjaxRequest();
 
 describe('Unit | Mixin | legacy/normalize error response', function() {
-  it('formats the error response according to the legacy format', function() {
-    const service = new AjaxRequest();
-
+  it('handles JSON:API formatted error objects', function() {
     const jsonApiError = service.normalizeErrorResponse(400, {}, {
       errors: [
         { status: 400, title: 'Foo' },
@@ -20,7 +19,9 @@ describe('Unit | Mixin | legacy/normalize error response', function() {
         { status: '400', title: 'Foo' },
         { status: '400', title: 'Foo' }
     ]);
+  });
 
+  it('handles an object with an array of error strings', function() {
     const payloadWithErrorStrings = service.normalizeErrorResponse(400, {}, {
       errors: [
         'This is an error',
@@ -31,7 +32,9 @@ describe('Unit | Mixin | legacy/normalize error response', function() {
       { status: '400', title: 'This is an error' },
       { status: '400', title: 'This is another error' }
     ]);
+  });
 
+  it('handles an array of error objects', function() {
     const payloadArrayOfObjects = service.normalizeErrorResponse(400, {}, [
       { status: 400, title: 'Foo' },
       { status: 400, title: 'Bar' }
@@ -40,23 +43,30 @@ describe('Unit | Mixin | legacy/normalize error response', function() {
       { status: '400', title: 'Foo', detail: { status: 400, title: 'Foo' } },
       { status: '400', title: 'Bar', detail: { status: 400, title: 'Bar' } }
     ]);
+  });
 
+  it('handles an array of strings', function() {
     const payloadArrayOfStrings = service.normalizeErrorResponse(400, {}, [
       'Foo', 'Bar'
     ]);
     expect(payloadArrayOfStrings).to.deep.equal([
       { status: '400', title: 'Foo' },
       { status: '400', title: 'Bar' }
     ]);
+  });
 
+  it('handles a string', function() {
     const payloadIsString = service.normalizeErrorResponse(400, {}, 'Foo');
+
     expect(payloadIsString).to.deep.equal([
       {
         status: '400',
         title: 'Foo'
       }
     ]);
+  });
 
+  it('handles an arbitrary object', function() {
     const payloadIsObject = service.normalizeErrorResponse(400, {}, {
       title: 'Foo'
     });