fix: HttpParams and HttpHeaders are immutable!

src/app/http-client/http-client-feature.service.spec.ts

@@ -1,5 +1,5 @@
 import { TestBed, async, inject } from '@angular/core/testing';
-import { HttpClientModule, HttpRequest } from '@angular/common/http';
+import { HttpClientModule, HttpRequest, HttpParams } from '@angular/common/http';
 import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';
 import { HttpClientFeatureService } from './http-client-feature.service';
 
@@ -26,10 +26,14 @@ describe(`HttpClientFeatureService`, () => {
       service.login('foo', 'bar').subscribe();
 
       backend.expectOne((req: HttpRequest<any>) => {
-        return req.url === 'auth/login' &&
-          req.method === 'POST' &&
-          req.headers.get('Content-Type') === 'application/x-www-form-urlencoded';
-      }, 'Login Request');
+        const body = new HttpParams({ fromString: req.body });
+
+        return req.url === 'auth/login'
+          && req.method === 'POST'
+          && req.headers.get('Content-Type') === 'application/x-www-form-urlencoded'
+          && body.get('user') === 'foo'
+          && body.get('password') === 'bar';
+      }, `POST to 'auth/login' with form-encoded user and password`);
   })));
 
   it(`should emit 'false' for 401 Unauthorized`, async(inject([HttpClientFeatureService, HttpTestingController],

src/app/http-client/http-client-feature.service.ts

@@ -11,12 +11,12 @@ export class HttpClientFeatureService {
   ) {}
 
   login(user: string, password: string): Observable<boolean> {
-    const body = new HttpParams();
-    body.set(`user`, user);
-    body.set(`password`, password);
+    const body = new HttpParams()
+      .set(`user`, user)
+      .set(`password`, password);
     const headers = new HttpHeaders({ 'Content-Type': 'application/x-www-form-urlencoded' });
 
-    return this.http.post(`auth/login`, body.toString, { headers, observe: 'response' })
+    return this.http.post(`auth/login`, body.toString(), { headers, observe: 'response' })
       .map((res: HttpResponse<Object>) => res.ok)
       .catch((err: any) => Observable.of(false));
   }