Angular5 / ng test ERROR : TypeError: this.handler.handle is not a function

This is my Angular configuration :

Angular CLI: 1.7.2
Node: 6.10.0
OS: win32 x64
Angular: 5.2.5
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router

@angular/cli: 1.7.2
@angular-devkit/build-optimizer: 0.3.2
@angular-devkit/core: 0.3.2
@angular-devkit/schematics: 0.3.2
@ngtools/json-schema: 1.2.0
@ngtools/webpack: 1.10.1
@schematics/angular: 0.3.2
@schematics/package-update: 0.3.2
typescript: 2.6.2
webpack: 3.11.0


My package.json file :

{
"name": "xxxx",
"version": "0.0.0",
"license": "MIT",
"scripts": {
"ng": "ng",
"start": "ng serve --proxy-config proxy.conf.json",
"build": "ng build --prod",
"test": "ng test",
"lint": "ng lint",
"e2e": "ng e2e",
"ng2ninja": "ng2ninja"
},
"private": true,
"dependencies": {
"@angular/animations": "5.2.5",
"@angular/common": "5.2.5",
"@angular/compiler": "5.2.5",
"@angular/core": "5.2.5",
"@angular/forms": "5.2.5",
"@angular/platform-browser": "5.2.5",
"@angular/platform-browser-dynamic": "5.2.5",
"@angular/router": "5.2.5",
"@ng-bootstrap/ng-bootstrap": "^1.0.0",
"bootstrap": "4.0.0",
"core-js": "2.4.1",
"font-awesome": "4.7.0",
"rxjs": "5.5.6",
"tslint-sonarts": "^1.6.0",
"yarn": "^1.5.1",
"zone.js": "0.8.19"
},
"devDependencies": {
"@angular/cli": "^1.7.1",
"@angular/compiler-cli": "5.2.5",
"@angular/language-service": "5.2.5",
"@types/jasmine": "2.8.6",
"@types/jasminewd2": "2.0.3",
"@types/node": "8.5.2",
"@ng-bootstrap/ng-bootstrap": "1.0.0",
"angular-ide": "^0.9.39",
"codelyzer": "4.1.0",
"jasmine-core": "2.8.0",
"jasmine-spec-reporter": "4.2.1",
"karma": "2.0.0",
"karma-chrome-launcher": "2.2.0",
"karma-coverage-istanbul-reporter": "1.3.3",
"karma-firefox-launcher": "1.1.0",
"karma-jasmine": "1.1.1",
"karma-jasmine-html-reporter": "0.2.2",
"karma-json-reporter": "1.2.1",
"ng2ninja": "1.0.17",
"protractor": "5.2.2",
"ts-node": "4.1.0",
"tslint": "5.9.1",
"typescript": "2.6.2"
}
}


I obtain this error message when i run the command 'ng test' :

TypeError: this.handler.handle is not a function
at MergeMapSubscriber.__WEBPACK_IMPORTED_MODULE_2_rxjs_operator_concatMap__.a.call [as project] node_modules/@angular/common/esm2015/http.js:1174:28)
at MergeMapSubscriber._tryNext node_modules/rxjs/_esm2015/operators/mergeMap.js:109:1)
at MergeMapSubscriber._next node_modules/rxjs/_esm2015/operators/mergeMap.js:99:1)
at MergeMapSubscriber.next node_modules/rxjs/_esm2015/Subscriber.js:83:1)
at ScalarObservable._subscribe node_modules/rxjs/_esm2015/observable/ScalarObservable.js:42:1)
at ScalarObservable._trySubscribe node_modules/rxjs/_esm2015/Observable.js:171:1)
at ScalarObservable.subscribe node_modules/rxjs/_esm2015/Observable.js:159:1)
at MergeMapOperator.call node_modules/rxjs/_esm2015/operators/mergeMap.js:78:1)
at Observable.subscribe node_modules/rxjs/_esm2015/Observable.js:156:1)


This is my test:

import {TestBed, inject} from '@angular/core/testing';
import {HttpClientTestingModule, HttpTestingController} from '@angular/common/http/testing';
import {UserService} from './user.service';
import {environment} from '../environments/environment';
import {JwtInterceptorService} from './jwt-interceptor.service';
import {User} from './services/model/user';
import {HttpClient, HttpHandler} from '@angular/common/http';
...
it('should authenticate a user', () => {
// spy on the store method
spyOn(userService, 'storeLoggedInUser');

const credentials = {login: 'toto', password: 'titi'};
let actualUser;
userService.login(credentials).subscribe(fetchedUser => actualUser = fetchedUser);
...
});


After analyze and debug, the problem comes from the call of the "login" method of the User Service.

Having browsed of numerous post (and solutions) i do not understand the real origin of my error message.

This is my User Service :

login(credentials): Observable<User> {
var headers = new HttpHeaders();
headers.append('Content-Type', 'application/x-www-form-urlencoded');

var paramCredentials = "grant_type=password"
+ "&credentials=true"
+ "&scope=read write"
+ "&accept=application/json"
+ "&username=" + credentials.username
+ "&password=" + credentials.password;

return this.http.post<User>(`${environment.oAuthUrl}/oauth/token`, paramCredentials, {headers: headers}).pipe(
tap(user => this.storeLoggedInUser(user))
);
}

storeLoggedInUser(user) {
window.localStorage.setItem('jwtToken', JSON.stringify(user));
this.jwtInterceptorService.setJwtToken(user.token);
}


Any ideas ?

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