feat: support ngOnChanges with correct simple change object within rerender

ref testing-library#365

Author: shaman-apprentice

projects/testing-library/src/lib/models.ts

@@ -55,7 +55,7 @@ export interface RenderResult<ComponentType, WrapperType = ComponentType> extend
   /**
    * @description
    * Re-render the same component with different properties.
-   * This creates a new instance of the component.
+   * Properties not passed in again are removed.
    */
   rerender: (
     properties?: Pick<

projects/testing-library/src/lib/testing-library.ts

@@ -123,14 +123,38 @@ export async function render<SutType, WrapperType = SutType>(
 
   await renderFixture(componentProperties, componentInputs, componentOutputs);
 
+  let renderedPropKeys = Object.keys(componentProperties);
+  let renderedInputKeys = Object.keys(componentInputs);
+  let renderedOutputKeys = Object.keys(componentOutputs);
   const rerender = async (
     properties?: Pick<RenderTemplateOptions<SutType>, 'componentProperties' | 'componentInputs' | 'componentOutputs'>,
   ) => {
-    await renderFixture(
-      properties?.componentProperties ?? {},
-      properties?.componentInputs ?? {},
-      properties?.componentOutputs ?? {},
-    );
+    const newComponentInputs = properties?.componentInputs ?? {};
+    for (const inputKey of renderedInputKeys) {
+      if (!Object.prototype.hasOwnProperty.call(newComponentInputs, inputKey)) {
+        delete (fixture.componentInstance as any)[inputKey];
+      }
+    }
+    setComponentInputs(fixture, newComponentInputs);
+    renderedInputKeys = Object.keys(newComponentInputs);
+
+    const newComponentOutputs = properties?.componentOutputs ?? {};
+    for (const outputKey of renderedOutputKeys) {
+      if (!Object.prototype.hasOwnProperty.call(newComponentOutputs, outputKey)) {
+        delete (fixture.componentInstance as any)[outputKey];
+      }
+    }
+    setComponentOutputs(fixture, newComponentOutputs);
+    renderedOutputKeys = Object.keys(newComponentOutputs);
+
+    const newComponentProps = properties?.componentProperties ?? {};
+    const changes = updateProps(fixture, renderedPropKeys, newComponentProps);
+    if (hasOnChangesHook(fixture.componentInstance)) {
+      fixture.componentInstance.ngOnChanges(changes);
+    }
+    renderedPropKeys = Object.keys(newComponentProps);
+
+    fixture.componentRef.injector.get(ChangeDetectorRef).detectChanges();
   };
 
   const changeInput = (changedInputProperties: Partial<SutType>) => {
@@ -360,6 +384,31 @@ function getChangesObj(oldProps: Record<string, any> | null, newProps: Record<st
   );
 }
 
+function updateProps<SutType>(
+  fixture: ComponentFixture<SutType>,
+  prevRenderedPropsKeys: string[],
+  newProps: Record<string, any>,
+) {
+  const componentInstance = fixture.componentInstance as Record<string, any>;
+  const simpleChanges: SimpleChanges = {};
+
+  for (const key of prevRenderedPropsKeys) {
+    if (!Object.prototype.hasOwnProperty.call(newProps, key)) {
+      simpleChanges[key] = new SimpleChange(componentInstance[key], undefined, false);
+      delete componentInstance[key];
+    }
+  }
+
+  for (const [key, value] of Object.entries(newProps)) {
+    if (value !== componentInstance[key]) {
+      simpleChanges[key] = new SimpleChange(componentInstance[key], value, false);
+    }
+  }
+  setComponentProperties(fixture, newProps);
+
+  return simpleChanges;
+}
+
 function addAutoDeclarations<SutType>(
   sut: Type<SutType> | string,
   {

projects/testing-library/tests/rerender.spec.ts

@@ -1,15 +1,23 @@
-import { Component, Input } from '@angular/core';
+import { Component, Input, OnChanges, SimpleChanges } from '@angular/core';
 import { render, screen } from '../src/public_api';
 
+let ngOnChangesSpy: jest.Mock;
 @Component({
   selector: 'atl-fixture',
   template: ` {{ firstName }} {{ lastName }} `,
 })
-class FixtureComponent {
+class FixtureComponent implements OnChanges {
   @Input() firstName = 'Sarah';
   @Input() lastName?: string;
+  ngOnChanges(changes: SimpleChanges): void {
+    ngOnChangesSpy(changes);
+  }
 }
 
+beforeEach(() => {
+  ngOnChangesSpy = jest.fn();
+});
+
 test('rerenders the component with updated props', async () => {
   const { rerender } = await render(FixtureComponent);
   expect(screen.getByText('Sarah')).toBeInTheDocument();
@@ -54,6 +62,22 @@ test('rerenders the component with updated props and resets other props', async
   const firstName2 = 'Chris';
   await rerender({ componentProperties: { firstName: firstName2 } });
 
+  expect(screen.getByText(`${firstName2}`)).toBeInTheDocument();
   expect(screen.queryByText(`${firstName2} ${lastName}`)).not.toBeInTheDocument();
   expect(screen.queryByText(`${firstName} ${lastName}`)).not.toBeInTheDocument();
+
+  expect(ngOnChangesSpy).toHaveBeenCalledTimes(2); // one time initially and one time for rerender
+  const rerenderedChanges = ngOnChangesSpy.mock.calls[1][0] as SimpleChanges;
+  expect(rerenderedChanges).toEqual({
+    lastName: {
+      previousValue: 'Peeters',
+      currentValue: undefined,
+      firstChange: false,
+    },
+    firstName: {
+      previousValue: 'Mark',
+      currentValue: 'Chris',
+      firstChange: false,
+    },
+  });
 });