diff --git a/packages/language-service/test/completions_spec.ts b/packages/language-service/test/completions_spec.ts
index 70d205fe68..b1163d93a3 100644
--- a/packages/language-service/test/completions_spec.ts
+++ b/packages/language-service/test/completions_spec.ts
@@ -152,10 +152,9 @@ describe('completions', () => {
   });
 
   it('should respect paths configuration', () => {
-    mockHost.overrideOptions(options => {
-      options.baseUrl = '/app';
-      options.paths = {'bar/*': ['foo/bar/*']};
-      return options;
+    mockHost.overrideOptions({
+      baseUrl: '/app',
+      paths: {'bar/*': ['foo/bar/*']},
     });
     mockHost.addScript('/app/foo/bar/shared.ts', `
       export interface Node {
diff --git a/packages/language-service/test/diagnostics_spec.ts b/packages/language-service/test/diagnostics_spec.ts
index b017e7284a..d0ffac41cf 100644
--- a/packages/language-service/test/diagnostics_spec.ts
+++ b/packages/language-service/test/diagnostics_spec.ts
@@ -191,7 +191,7 @@ describe('diagnostics', () => {
     expect(() => ngLS.getDiagnostics(fileName)).not.toThrow();
   });
 
-  it('should not report an error for sub-types of string', () => {
+  it('should not report an error for sub-types of string in non-strict mode', () => {
     const fileName = '/app/app.component.ts';
     mockHost.override(fileName, `
       import { Component } from '@angular/core';
@@ -202,13 +202,16 @@ describe('diagnostics', () => {
       export class AppComponent {
         something: 'foo' | 'bar';
       }`);
+    mockHost.overrideOptions({
+      strict: false,  // TODO: this test fails in strict mode
+    });
     const tsDiags = tsLS.getSemanticDiagnostics(fileName);
     expect(tsDiags).toEqual([]);
     const ngDiags = ngLS.getDiagnostics(fileName);
     expect(ngDiags).toEqual([]);
   });
 
-  it('should not report an error for sub-types of number', () => {
+  it('should not report an error for sub-types of number in non-strict mode', () => {
     const fileName = '/app/app.component.ts';
     mockHost.override(fileName, `
       import { Component } from '@angular/core';
@@ -219,6 +222,9 @@ describe('diagnostics', () => {
       export class AppComponent {
         something: 123 | 456;
       }`);
+    mockHost.overrideOptions({
+      strict: false,  // TODO: This test fails in strict mode
+    });
     const tsDiags = tsLS.getSemanticDiagnostics(fileName);
     expect(tsDiags).toEqual([]);
     const ngDiags = ngLS.getDiagnostics(fileName);
@@ -233,7 +239,7 @@ describe('diagnostics', () => {
       @Component({
         template: '<div (click)="onClick"></div>'
       })
-      export class MyComponent {
+      export class AppComponent {
         onClick() { }
       }`);
     const diagnostics = ngLS.getDiagnostics(fileName) !;
@@ -245,7 +251,7 @@ describe('diagnostics', () => {
   });
 
   // #13412
-  it('should not report an error for using undefined', () => {
+  it('should not report an error for using undefined under non-strict mode', () => {
     const fileName = '/app/app.component.ts';
     mockHost.override(fileName, `
       import { Component } from '@angular/core';
@@ -256,6 +262,9 @@ describe('diagnostics', () => {
       export class AppComponent {
         something = 'foo';
       }`);
+    mockHost.overrideOptions({
+      strict: false,  // TODO: This test fails in strict mode
+    });
     const tsDiags = tsLS.getSemanticDiagnostics(fileName);
     expect(tsDiags).toEqual([]);
     const ngDiags = ngLS.getDiagnostics(fileName);
@@ -342,7 +351,10 @@ describe('diagnostics', () => {
       })
       export class AppComponent {}`);
     const tsDiags = tsLS.getSemanticDiagnostics(fileName);
-    expect(tsDiags).toEqual([]);
+    expect(tsDiags.length).toBe(1);
+    const msgText = ts.flattenDiagnosticMessageText(tsDiags[0].messageText, '\n');
+    expect(msgText).toBe(
+        `Type 'null[]' is not assignable to type 'Provider[]'.\n  Type 'null' is not assignable to type 'Provider'.`);
     const ngDiags = ngLS.getDiagnostics(fileName);
     expect(ngDiags.length).toBe(1);
     const {messageText, start, length} = ngDiags[0];
@@ -391,7 +403,7 @@ describe('diagnostics', () => {
         \`
       })
       export class AppComponent {
-        fieldCount: number;
+        fieldCount: number = 0;
       }`);
     const tsDiags = tsLS.getSemanticDiagnostics(fileName);
     expect(tsDiags).toEqual([]);
@@ -401,9 +413,8 @@ describe('diagnostics', () => {
 
   // Issue #15885
   it('should be able to remove null and undefined from a type', () => {
-    mockHost.overrideOptions(options => {
-      options.strictNullChecks = true;
-      return options;
+    mockHost.overrideOptions({
+      strictNullChecks: true,
     });
     const fileName = '/app/app.component.ts';
     mockHost.override(fileName, `
@@ -441,9 +452,8 @@ describe('diagnostics', () => {
         onSubmit(form: NgForm) {}
       }`);
     mockHost.addScript('/other/files/app/server.ts', 'export class Server {}');
-    mockHost.overrideOptions(options => {
-      options.baseUrl = '/other/files';
-      return options;
+    mockHost.overrideOptions({
+      baseUrl: '/other/files',
     });
     const tsDiags = tsLS.getSemanticDiagnostics(fileName);
     expect(tsDiags).toEqual([]);
@@ -568,10 +578,13 @@ describe('diagnostics', () => {
     it('should not report errors for valid styleUrls', () => {
       const fileName = '/app/app.component.ts';
       mockHost.override(fileName, `
+        import {Component} from '@angular/core';
+
         @Component({
+          template: '<div></div>',
           styleUrls: ['./test.css', './test.css'],
         })
-        export class MyComponent {}`);
+        export class AppComponent {}`);
 
       const diagnostics = ngLS.getDiagnostics(fileName) !;
       expect(diagnostics.length).toBe(0);
diff --git a/packages/language-service/test/project/app/app.component.ts b/packages/language-service/test/project/app/app.component.ts
index 36a97d5055..d6cbb73f70 100644
--- a/packages/language-service/test/project/app/app.component.ts
+++ b/packages/language-service/test/project/app/app.component.ts
@@ -8,7 +8,7 @@
 
 import {Component} from '@angular/core';
 
-export class Hero {
+export interface Hero {
   id: number;
   name: string;
 }
@@ -30,5 +30,5 @@ export class Hero {
 export class AppComponent {
   title = 'Tour of Heroes';
   hero: Hero = {id: 1, name: 'Windstorm'};
-  private internal: string;
+  private internal: string = 'internal';
 }
diff --git a/packages/language-service/test/project/app/expression-cases.ts b/packages/language-service/test/project/app/expression-cases.ts
index 7dd2cacf36..84a78f2abb 100644
--- a/packages/language-service/test/project/app/expression-cases.ts
+++ b/packages/language-service/test/project/app/expression-cases.ts
@@ -44,5 +44,5 @@ export class ExpectNumericType {
   template: '{{ (name | lowercase).~{string-pipe}substring }}',
 })
 export class LowercasePipe {
-  name: string;
+  name: string = 'name';
 }
diff --git a/packages/language-service/test/project/app/ng-for-cases.ts b/packages/language-service/test/project/app/ng-for-cases.ts
index 1515c2ab2f..806daf5730 100644
--- a/packages/language-service/test/project/app/ng-for-cases.ts
+++ b/packages/language-service/test/project/app/ng-for-cases.ts
@@ -29,7 +29,7 @@ export class UnknownPeople {
     </div>`,
 })
 export class UnknownEven {
-  people: Person[];
+  people: Person[] = [];
 }
 
 @Component({
@@ -39,5 +39,5 @@ export class UnknownEven {
     </div>`,
 })
 export class UnknownTrackBy {
-  people: Person[];
+  people: Person[] = [];
 }
diff --git a/packages/language-service/test/project/app/parsing-cases.ts b/packages/language-service/test/project/app/parsing-cases.ts
index 3fcf215fcd..cd9fa37a4d 100644
--- a/packages/language-service/test/project/app/parsing-cases.ts
+++ b/packages/language-service/test/project/app/parsing-cases.ts
@@ -49,21 +49,21 @@ export class NoValueAttribute {
   template: '<h1 model="~{attribute-binding-model}test"></h1>',
 })
 export class AttributeBinding {
-  test: string;
+  test: string = 'test';
 }
 
 @Component({
   template: '<h1 [model]="~{property-binding-model}test"></h1>',
 })
 export class PropertyBinding {
-  test: string;
+  test: string = 'test';
 }
 
 @Component({
   template: '<h1 (model)="~{event-binding-model}modelChanged()"></h1>',
 })
 export class EventBinding {
-  test: string;
+  test: string = 'test';
 
   modelChanged() {}
 }
@@ -72,23 +72,23 @@ export class EventBinding {
   template: '<h1 [(model)]="~{two-way-binding-model}test"></h1>',
 })
 export class TwoWayBinding {
-  test: string;
+  test: string = 'test';
 }
 
 @Directive({
   selector: '[string-model]',
 })
 export class StringModel {
-  @Input() model: string;
-  @Output() modelChanged: EventEmitter<string>;
+  @Input() model: string = 'model';
+  @Output() modelChanged: EventEmitter<string> = new EventEmitter();
 }
 
 @Directive({
   selector: '[number-model]',
 })
 export class NumberModel {
-  @Input('inputAlias') model: number;
-  @Output('outputAlias') modelChanged: EventEmitter<number>;
+  @Input('inputAlias') model: number = 0;
+  @Output('outputAlias') modelChanged: EventEmitter<number> = new EventEmitter();
 }
 
 interface Person {
@@ -122,7 +122,7 @@ export class ForLetIEqual {
     </div>`,
 })
 export class ForUsingComponent {
-  people: Person[];
+  people: Person[] = [];
 }
 
 @Component({
diff --git a/packages/language-service/test/project/tsconfig.json b/packages/language-service/test/project/tsconfig.json
new file mode 100644
index 0000000000..0e793bb214
--- /dev/null
+++ b/packages/language-service/test/project/tsconfig.json
@@ -0,0 +1,11 @@
+{
+  "//00": "This file is used for IDE only, actual compilation options is in MockTypescriptHost in test_utils.ts",
+  "compilerOptions": {
+    "strict": true,
+    "experimentalDecorators": true,
+    "baseUrl": "../../../..",
+    "paths": {
+      "@angular/*": ["packages/*"]
+    }
+  }
+}
diff --git a/packages/language-service/test/test_utils.ts b/packages/language-service/test/test_utils.ts
index 8f87737fd9..4bf5074054 100644
--- a/packages/language-service/test/test_utils.ts
+++ b/packages/language-service/test/test_utils.ts
@@ -79,6 +79,17 @@ function loadTourOfHeroes(): ReadonlyMap<string, string> {
 }
 
 const TOH = loadTourOfHeroes();
+const COMPILER_OPTIONS: Readonly<ts.CompilerOptions> = {
+  target: ts.ScriptTarget.ES5,
+  module: ts.ModuleKind.CommonJS,
+  moduleResolution: ts.ModuleResolutionKind.NodeJs,
+  emitDecoratorMetadata: true,
+  experimentalDecorators: true,
+  removeComments: false,
+  noImplicitAny: false,
+  lib: ['lib.es2015.d.ts', 'lib.dom.d.ts'],
+  strict: true,
+};
 
 export class MockTypescriptHost implements ts.LanguageServiceHost {
   private angularPath?: string;
@@ -98,16 +109,7 @@ export class MockTypescriptHost implements ts.LanguageServiceHost {
     const support = setup();
     this.nodeModulesPath = path.posix.join(support.basePath, 'node_modules');
     this.angularPath = path.posix.join(this.nodeModulesPath, '@angular');
-    this.options = {
-      target: ts.ScriptTarget.ES5,
-      module: ts.ModuleKind.CommonJS,
-      moduleResolution: ts.ModuleResolutionKind.NodeJs,
-      emitDecoratorMetadata: true,
-      experimentalDecorators: true,
-      removeComments: false,
-      noImplicitAny: false,
-      lib: ['lib.es2015.d.ts', 'lib.dom.d.ts'],
-    };
+    this.options = COMPILER_OPTIONS;
   }
 
   override(fileName: string, content: string) {
@@ -133,12 +135,12 @@ export class MockTypescriptHost implements ts.LanguageServiceHost {
 
   forgetAngular() { this.angularPath = undefined; }
 
-  overrideOptions(cb: (options: ts.CompilerOptions) => ts.CompilerOptions) {
-    this.options = cb((Object as any).assign({}, this.options));
+  overrideOptions(options: Partial<ts.CompilerOptions>) {
+    this.options = {...this.options, ...options};
     this.projectVersion++;
   }
 
-  getCompilationSettings(): ts.CompilerOptions { return this.options; }
+  getCompilationSettings(): ts.CompilerOptions { return {...this.options}; }
 
   getProjectVersion(): string { return this.projectVersion.toString(); }
 
@@ -199,6 +201,7 @@ export class MockTypescriptHost implements ts.LanguageServiceHost {
   reset() {
     this.overrides.clear();
     this.overrideDirectory.clear();
+    this.options = COMPILER_OPTIONS;
   }
 
   private getRawFileContent(fileName: string): string|undefined {