Angular Testing error - this._formBuilder.group is not a function

I have a standard function to register users. In the test file, I am getting the error:

TypeError: this._formBuilder.group is not a function

This seems to be from the ngOnInit function. I have tried importing the testing module numerous ways - as an empty object, etc. It seems as if this is where the problem is coming from. I could try to mock the FormBuilder, but that seems like something that should not be necessary as the function doesn't do any http work.

Typescript File :

import { Component, OnDestroy, OnInit, ViewEncapsulation } from '@angular/core';
import { AbstractControl, FormBuilder, FormGroup, ValidationErrors, ValidatorFn, Validators } from '@angular/forms';
import { Subject } from 'rxjs';
import { takeUntil } from 'rxjs/internal/operators';

import { FuseConfigService } from '@fuse/services/config.service';
import { fuseAnimations } from '@fuse/animations';

import { AuthService } from 'app/main/services/auth.service';

@Component({
    selector     : 'register',
    templateUrl  : './register.component.html',
    styleUrls    : ['./register.component.scss'],
    encapsulation: ViewEncapsulation.None,
    animations   : fuseAnimations
})
export class RegisterComponent implements OnInit, OnDestroy
{
    registerForm: FormGroup;

    // Private
    private _unsubscribeAll: Subject<any>;

    constructor(
        private _fuseConfigService: FuseConfigService,
        private _formBuilder: FormBuilder,
        public authService: AuthService
    )
    {
        // Configure the layout
        this._fuseConfigService.config = {
            layout: {
                navbar   : {
                    hidden: true
                },
                toolbar  : {
                    hidden: true
                },
                footer   : {
                    hidden: true
                },
                sidepanel: {
                    hidden: true
                }
            }
        };

        // Set the private defaults
        this._unsubscribeAll = new Subject();
    }



    // -----------------------------------------------------------------------------------------------------
    // @ Lifecycle hooks
    // -----------------------------------------------------------------------------------------------------

    /**
     * On init
     */
    ngOnInit(): void
    {
        this.registerForm = this._formBuilder.group({
            name           : ['', Validators.required],
            email          : ['', [Validators.required, Validators.email]],
            password       : ['', Validators.required],
            passwordConfirm: ['', [Validators.required, confirmPasswordValidator]]
        });

        // Update the validity of the 'passwordConfirm' field
        // when the 'password' field changes
        this.registerForm.get('password').valueChanges
            .pipe(takeUntil(this._unsubscribeAll))
            .subscribe(() => {
                this.registerForm.get('passwordConfirm').updateValueAndValidity();
            });
    }

    /**
     * On destroy
     */
    ngOnDestroy(): void
    {
        // Unsubscribe from all subscriptions
        this._unsubscribeAll.next();
        this._unsubscribeAll.complete();
    }
}

/**
 * Confirm password validator
 *
 * @param {AbstractControl} control
 * @returns {ValidationErrors | null}
 */
export const confirmPasswordValidator: ValidatorFn = (control: AbstractControl): ValidationErrors | null => {

    if ( !control.parent || !control )
    {
        return null;
    }

    const password = control.parent.get('password');
    const passwordConfirm = control.parent.get('passwordConfirm');

    if ( !password || !passwordConfirm )
    {
        return null;
    }

    if ( passwordConfirm.value === '' )
    {
        return null;
    }

    if ( password.value === passwordConfirm.value )
    {
        return null;
    }

    return {passwordsNotMatching: true};
};

Test file

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { RegisterComponent } from './register.component';
import { AbstractControl, FormBuilder, FormGroup, ValidationErrors, ValidatorFn, Validators } from '@angular/forms';
import { Subject } from 'rxjs';
import { takeUntil } from 'rxjs/internal/operators';
import { FuseConfigService } from '@fuse/services/config.service';
import { fuseAnimations } from '@fuse/animations';
import { AuthService } from 'app/main/services/auth.service';
import { ReactiveFormsModule } from '@angular/forms';


import { mockItems } from 'app/main/services/mockItems';

import { MatIconModule } from '@angular/material/icon';
import { MatFormFieldModule } from '@angular/material/form-field';
import { MatCheckboxModule } from '@angular/material/checkbox';



describe('RegisterComponent', () => {
    let component: RegisterComponent;
    let fixture: ComponentFixture<RegisterComponent>;


    let MockGroup = new mockItems();







    beforeEach(async(() => {
        TestBed.configureTestingModule({
            declarations: [ RegisterComponent ]
        })
        .compileComponents();
    }));




    beforeEach(() => {


        
        TestBed.configureTestingModule({
            imports: [ MatIconModule,
                       MatFormFieldModule,
                       MatCheckboxModule,
                       ReactiveFormsModule ],
            declarations: [ RegisterComponent ],
            providers: [ { provide: FuseConfigService,  useValue : {} },
                         { provide: FormBuilder,        useValue : FormBuilder },
                         { provide: AuthService,        useValue : {} } ]

        });


        fixture = TestBed.createComponent(RegisterComponent);
        component = fixture.componentInstance;
        fixture.detectChanges();
    });




    it('should create', () => {
        expect(component).toBeTruthy();
    });



});