mapAsyncIterator-test: replace 'invariant' with expect chains (#2679)

Author: IvanGoncharov

src/subscription/__tests__/mapAsyncIterator-test.js

@@ -3,8 +3,6 @@
 import { expect } from 'chai';
 import { describe, it } from 'mocha';
 
-import invariant from '../../jsutils/invariant';
-
 import mapAsyncIterator from '../mapAsyncIterator';
 
 describe('mapAsyncIterator', () => {
@@ -271,8 +269,9 @@ describe('mapAsyncIterator', () => {
       caughtError = e;
     }
 
-    invariant(caughtError != null);
-    expect(caughtError.message).to.equal('Goodbye');
+    expect(caughtError)
+      .to.be.an.instanceOf(Error)
+      .with.property('message', 'Goodbye');
   });
 
   it('maps over thrown errors if second callback provided', async () => {
@@ -293,8 +292,9 @@ describe('mapAsyncIterator', () => {
     });
 
     const result = await doubles.next();
-    invariant(result.value instanceof Error);
-    expect(result.value.message).to.equal('Goodbye');
+    expect(result.value)
+      .to.be.an.instanceOf(Error)
+      .with.property('message', 'Goodbye');
     expect(result.done).to.equal(false);
 
     expect(await doubles.next()).to.deep.equal({
@@ -330,8 +330,9 @@ describe('mapAsyncIterator', () => {
       expectedError = error;
     }
 
-    invariant(expectedError instanceof Error);
-    expect(expectedError.message).to.equal('Cannot count to 2');
+    expect(expectedError)
+      .to.be.an.instanceOf(Error)
+      .with.property('message', 'Cannot count to 2');
 
     expect(await throwOver1.next()).to.deep.equal({
       value: undefined,
@@ -375,8 +376,9 @@ describe('mapAsyncIterator', () => {
       expectedError = error;
     }
 
-    invariant(expectedError instanceof Error);
-    expect(expectedError.message).to.equal('Cannot count to 2');
+    expect(expectedError)
+      .to.be.an.instanceOf(Error)
+      .with.property('message', 'Cannot count to 2');
 
     expect(await throwOver1.next()).to.deep.equal({
       value: undefined,