[Translation service] Constrain service api (#2539)

* [translation-service] Delay `request`'s work in api.js

The "work" got executed immediately, and just the response was
delayed with setTimeout. The user could make a next fetch without
waiting for a response. Now the work itself is done in the timeout
callback, getting delayed too.

* [translation-service] Add `ConnectionError` error class

Any Error child class satisfied tests that expected
`toThrow(Error)`, meaning unintended behaviour still passed the
tests.

* [CI] Format code

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

exercises/concept/translation-service/.meta/config.json

@@ -3,7 +3,8 @@
     "SleeplessByte"
   ],
   "contributors": [
-    "AndrewLawendy"
+    "AndrewLawendy",
+    "themetar"
   ],
   "files": {
     "solution": [

exercises/concept/translation-service/api.js

@@ -1,4 +1,9 @@
-import { AbusiveClientError, NotAvailable, Untranslatable } from './errors';
+import {
+  AbusiveClientError,
+  NotAvailable,
+  Untranslatable,
+  ConnectionError,
+} from './errors';
 
 const mutex = { current: false };
 
@@ -85,13 +90,12 @@ export class ExternalApi {
     }
 
     if (this.values[text]) {
-      this.values[text].shift();
+      setTimeout(() => {
+        this.values[text].shift();
 
-      // If it's now available, yay, otherwise, nay
-      setTimeout(
-        () => callback(this.values[text][0] ? undefined : makeRandomError()),
-        1,
-      );
+        // If it's now available, yay, otherwise, nay
+        callback(this.values[text][0] ? undefined : makeRandomError());
+      }, 1);
       return;
     }
 
@@ -114,7 +118,7 @@ function rejectWithRandomDelay(value) {
 }
 
 function makeRandomError() {
-  return new Error(`Error code ${Math.ceil(Math.random() * 10000)}`);
+  return new ConnectionError(`Error code ${Math.ceil(Math.random() * 10000)}`);
 }
 
 class BadRequest extends Error {

exercises/concept/translation-service/errors.js

@@ -25,3 +25,9 @@ export class Untranslatable extends Error {
     super('jIyajbe’');
   }
 }
+
+export class ConnectionError extends Error {
+  constructor(message) {
+    super(message);
+  }
+}

exercises/concept/translation-service/service.spec.js

@@ -6,7 +6,7 @@ import {
   BatchIsEmpty,
 } from './service';
 
-import { NotAvailable, Untranslatable } from './errors';
+import { NotAvailable, Untranslatable, ConnectionError } from './errors';
 import { ExternalApi } from './api';
 
 describe('Free service', () => {
@@ -134,7 +134,7 @@ describe('Request service', () => {
   test('it requests at most three times (does not retry thrice or more)', async () => {
     const actual = service.request('ghobe’');
 
-    await expect(actual).rejects.toThrow(Error);
+    await expect(actual).rejects.toThrow(ConnectionError);
   });
 });
 
@@ -182,7 +182,7 @@ describe('Premium service', () => {
   test('it requests at most three times (does not retry thrice or more)', async () => {
     const actual = service.premium('ghobe’', 0);
 
-    await expect(actual).rejects.toThrow(Error);
+    await expect(actual).rejects.toThrow(ConnectionError);
   });
 
   test('it recognizes sufficient quality', async () => {