refactor(core): ensure compatibility with typescript strict flag (#30993)

As part of FW-1265, the `@angular/core` package is made compatible
with the TypeScript `--strict` flag. This already unveiled a few bugs,
so the strictness flag seems to help with increasing the overall code health.

Read more about the strict flag [here](https://www.typescriptlang.org/docs/handbook/compiler-options.html)

PR Close #30993

packages/core/testing/src/async_fallback.ts

@@ -36,7 +36,7 @@ export function asyncFallback(fn: Function): (done: any) => any {
   // function when asynchronous activity is finished.
   if (_global.jasmine) {
     // Not using an arrow function to preserve context passed from call site
-    return function(done: any) {
+    return function(this: unknown, done: any) {
       if (!done) {
         // if we run beforeEach in @angular/core/testing/testing_internal then we get no done
         // fake it here and assume sync.
@@ -56,7 +56,7 @@ export function asyncFallback(fn: Function): (done: any) => any {
   // is finished. This will be correctly consumed by the Mocha framework with
   // it('...', async(myFn)); or can be used in a custom framework.
   // Not using an arrow function to preserve context passed from call site
-  return function() {
+  return function(this: unknown) {
     return new Promise<void>((finishCallback, failCallback) => {
       runInTestZone(fn, this, finishCallback, failCallback);
     });

packages/core/testing/src/fake_async_fallback.ts

@@ -55,7 +55,7 @@ let _inFakeAsyncCall = false;
  */
 export function fakeAsyncFallback(fn: Function): (...args: any[]) => any {
   // Not using an arrow function to preserve context passed from call site
-  return function(...args: any[]) {
+  return function(this: unknown, ...args: any[]) {
     const proxyZoneSpec = ProxyZoneSpec.assertPresent();
     if (_inFakeAsyncCall) {
       throw new Error('fakeAsync() calls can not be nested');

packages/core/testing/src/r3_test_bed_compiler.ts

@@ -517,20 +517,21 @@ export class R3TestBedCompiler {
       op.def[op.field] = op.original;
     }
     // Restore initial component/directive/pipe defs
-    this.initialNgDefs.forEach((value: [string, PropertyDescriptor], type: Type<any>) => {
-      const [prop, descriptor] = value;
-      if (!descriptor) {
-        // Delete operations are generally undesirable since they have performance implications
-        // on objects they were applied to. In this particular case, situations where this code is
-        // invoked should be quite rare to cause any noticable impact, since it's applied only to
-        // some test cases (for example when class with no annotations extends some @Component)
-        // when we need to clear 'ngComponentDef' field on a given class to restore its original
-        // state (before applying overrides and running tests).
-        delete (type as any)[prop];
-      } else {
-        Object.defineProperty(type, prop, descriptor);
-      }
-    });
+    this.initialNgDefs.forEach(
+        (value: [string, PropertyDescriptor | undefined], type: Type<any>) => {
+          const [prop, descriptor] = value;
+          if (!descriptor) {
+            // Delete operations are generally undesirable since they have performance implications
+            // on objects they were applied to. In this particular case, situations where this code
+            // is invoked should be quite rare to cause any noticeable impact, since it's applied
+            // only to some test cases (for example when class with no annotations extends some
+            // @Component) when we need to clear 'ngComponentDef' field on a given class to restore
+            // its original state (before applying overrides and running tests).
+            delete (type as any)[prop];
+          } else {
+            Object.defineProperty(type, prop, descriptor);
+          }
+        });
     this.initialNgDefs.clear();
     this.moduleProvidersOverridden.clear();
     this.restoreComponentResolutionQueue();

packages/core/testing/src/test_bed.ts

@@ -654,7 +654,7 @@ export function inject(tokens: any[], fn: Function): () => any {
   const testBed = getTestBed();
   if (tokens.indexOf(AsyncTestCompleter) >= 0) {
     // Not using an arrow function to preserve context passed from call site
-    return function() {
+    return function(this: unknown) {
       // Return an async test method that returns a Promise if AsyncTestCompleter is one of
       // the injected tokens.
       return testBed.compileComponents().then(() => {
@@ -665,7 +665,7 @@ export function inject(tokens: any[], fn: Function): () => any {
     };
   } else {
     // Not using an arrow function to preserve context passed from call site
-    return function() { return testBed.execute(tokens, fn, this); };
+    return function(this: unknown) { return testBed.execute(tokens, fn, this); };
   }
 }
 
@@ -685,7 +685,7 @@ export class InjectSetupWrapper {
   inject(tokens: any[], fn: Function): () => any {
     const self = this;
     // Not using an arrow function to preserve context passed from call site
-    return function() {
+    return function(this: unknown) {
       self._addModule();
       return inject(tokens, fn).call(this);
     };
@@ -701,7 +701,7 @@ export function withModule(moduleDef: TestModuleMetadata, fn?: Function | null):
     InjectSetupWrapper {
   if (fn) {
     // Not using an arrow function to preserve context passed from call site
-    return function() {
+    return function(this: unknown) {
       const testBed = getTestBed();
       if (moduleDef) {
         testBed.configureTestingModule(moduleDef);

packages/core/testing/src/testing_internal.ts

@@ -39,6 +39,8 @@ const globalTimeOut = jasmine.DEFAULT_TIMEOUT_INTERVAL;
 
 const testBed = getTestBed();
 
+export type TestFn = ((done: DoneFn) => any) | (() => any);
+
 /**
  * Mechanism to run `beforeEach()` functions of Angular tests.
  *
@@ -112,8 +114,7 @@ export function beforeEachProviders(fn: Function): void {
 }
 
 
-function _it(
-    jsmFn: Function, testName: string, testFn: (done?: DoneFn) => any, testTimeout = 0): void {
+function _it(jsmFn: Function, testName: string, testFn: TestFn, testTimeout = 0): void {
   if (runnerStack.length == 0) {
     // This left here intentionally, as we should never get here, and it aids debugging.
     // tslint:disable-next-line
@@ -135,7 +136,9 @@ function _it(
     runner.run();
 
     if (testFn.length === 0) {
-      const retVal = testFn();
+      // TypeScript doesn't infer the TestFn type without parameters here, so we
+      // need to manually cast it.
+      const retVal = (testFn as() => any)();
       if (isPromise(retVal)) {
         // Asynchronous test function that returns a Promise - wait for completion.
         retVal.then(done, done.fail);
@@ -150,15 +153,15 @@ function _it(
   }, timeout);
 }
 
-export function it(expectation: string, assertion: (done: DoneFn) => any, timeout?: number): void {
+export function it(expectation: string, assertion: TestFn, timeout?: number): void {
   return _it(jsmIt, expectation, assertion, timeout);
 }
 
-export function fit(expectation: string, assertion: (done: DoneFn) => any, timeout?: number): void {
+export function fit(expectation: string, assertion: TestFn, timeout?: number): void {
   return _it(jsmFIt, expectation, assertion, timeout);
 }
 
-export function xit(expectation: string, assertion: (done: DoneFn) => any, timeout?: number): void {
+export function xit(expectation: string, assertion: TestFn, timeout?: number): void {
   return _it(jsmXIt, expectation, assertion, timeout);
 }