Just added blank main, center, and left components

src/app/app.module.ts

@@ -6,11 +6,17 @@ import { AppComponent } from './app.component';
 import { TreeComponent } from './tree/tree.component';
 import {ButtonModule, MessageService, TreeModule} from 'primeng/primeng';
 import {HttpClientModule} from '@angular/common/http';
+import { MainComponent } from './main/main.component';
+import { CenterComponent } from './center/center.component';
+import { LeftComponent } from './left/left.component';
 
 @NgModule({
   declarations: [
     AppComponent,
-    TreeComponent
+    TreeComponent,
+    MainComponent,
+    CenterComponent,
+    LeftComponent
   ],
   imports: [
     BrowserModule,

src/app/center/center.component.html

@@ -0,0 +1 @@
+<p>center works!</p>

src/app/center/center.component.spec.ts

@@ -0,0 +1,25 @@
+import { async, ComponentFixture, TestBed } from '@angular/core/testing';
+
+import { CenterComponent } from './center.component';
+
+describe('CenterComponent', () => {
+  let component: CenterComponent;
+  let fixture: ComponentFixture<CenterComponent>;
+
+  beforeEach(async(() => {
+    TestBed.configureTestingModule({
+      declarations: [ CenterComponent ]
+    })
+    .compileComponents();
+  }));
+
+  beforeEach(() => {
+    fixture = TestBed.createComponent(CenterComponent);
+    component = fixture.componentInstance;
+    fixture.detectChanges();
+  });
+
+  it('should create', () => {
+    expect(component).toBeTruthy();
+  });
+});

src/app/center/center.component.ts

@@ -0,0 +1,15 @@
+import { Component, OnInit } from '@angular/core';
+
+@Component({
+  selector: 'app-center',
+  templateUrl: './center.component.html',
+  styleUrls: ['./center.component.css']
+})
+export class CenterComponent implements OnInit {
+
+  constructor() { }
+
+  ngOnInit() {
+  }
+
+}

src/app/left/left.component.html

@@ -0,0 +1 @@
+<p>left works!</p>

src/app/left/left.component.spec.ts

@@ -0,0 +1,25 @@
+import { async, ComponentFixture, TestBed } from '@angular/core/testing';
+
+import { LeftComponent } from './left.component';
+
+describe('LeftComponent', () => {
+  let component: LeftComponent;
+  let fixture: ComponentFixture<LeftComponent>;
+
+  beforeEach(async(() => {
+    TestBed.configureTestingModule({
+      declarations: [ LeftComponent ]
+    })
+    .compileComponents();
+  }));
+
+  beforeEach(() => {
+    fixture = TestBed.createComponent(LeftComponent);
+    component = fixture.componentInstance;
+    fixture.detectChanges();
+  });
+
+  it('should create', () => {
+    expect(component).toBeTruthy();
+  });
+});

src/app/left/left.component.ts

@@ -0,0 +1,15 @@
+import { Component, OnInit } from '@angular/core';
+
+@Component({
+  selector: 'app-left',
+  templateUrl: './left.component.html',
+  styleUrls: ['./left.component.css']
+})
+export class LeftComponent implements OnInit {
+
+  constructor() { }
+
+  ngOnInit() {
+  }
+
+}

src/app/main/main.component.html

@@ -0,0 +1 @@
+<p>main works!</p>

src/app/main/main.component.spec.ts

@@ -0,0 +1,25 @@
+import { async, ComponentFixture, TestBed } from '@angular/core/testing';
+
+import { MainComponent } from './main.component';
+
+describe('MainComponent', () => {
+  let component: MainComponent;
+  let fixture: ComponentFixture<MainComponent>;
+
+  beforeEach(async(() => {
+    TestBed.configureTestingModule({
+      declarations: [ MainComponent ]
+    })
+    .compileComponents();
+  }));
+
+  beforeEach(() => {
+    fixture = TestBed.createComponent(MainComponent);
+    component = fixture.componentInstance;
+    fixture.detectChanges();
+  });
+
+  it('should create', () => {
+    expect(component).toBeTruthy();
+  });
+});

src/app/main/main.component.ts

@@ -0,0 +1,15 @@
+import { Component, OnInit } from '@angular/core';
+
+@Component({
+  selector: 'app-main',
+  templateUrl: './main.component.html',
+  styleUrls: ['./main.component.css']
+})
+export class MainComponent implements OnInit {
+
+  constructor() { }
+
+  ngOnInit() {
+  }
+
+}

src/app/tree/tree.component.html

@@ -1,6 +1,16 @@
-
 <p-tree #expandingTree [value]="filesTree"></p-tree>
 <div style="margin-top: 8px">
-  <button pButton type="button" label="Expand all" (click)="expandAll()" style="margin-right: .25em"></button>
-  <button pButton type="button" label="Collapse all" (click)="collapseAll()"></button>
+  <button
+    pButton
+    type="button"
+    label="Expand all"
+    (click)="expandAll()"
+    style="margin-right: .25em"
+  ></button>
+  <button
+    pButton
+    type="button"
+    label="Collapse all"
+    (click)="collapseAll()"
+  ></button>
 </div>

src/app/tree/tree.component.spec.ts

@@ -1,16 +1,15 @@
-import { async, ComponentFixture, TestBed } from '@angular/core/testing';
+import { async, ComponentFixture, TestBed } from "@angular/core/testing";
 
-import { TreeComponent } from './tree.component';
+import { TreeComponent } from "./tree.component";
 
-describe('TreeComponent', () => {
+describe("TreeComponent", () => {
   let component: TreeComponent;
   let fixture: ComponentFixture<TreeComponent>;
 
   beforeEach(async(() => {
     TestBed.configureTestingModule({
-      declarations: [ TreeComponent ]
-    })
-    .compileComponents();
+      declarations: [TreeComponent]
+    }).compileComponents();
   }));
 
   beforeEach(() => {
@@ -19,7 +18,7 @@ describe('TreeComponent', () => {
     fixture.detectChanges();
   });
 
-  it('should create', () => {
+  it("should create", () => {
     expect(component).toBeTruthy();
   });
 });