Ensure assertion template children are immutable (#587)

* Failing unit test for mutable children

* package-lock

* Ensure children are not able to be mutated when using the children and sibling apis

src/testing/assertionTemplate.ts

@@ -121,18 +121,19 @@ export function assertionTemplate(renderFunc: () => DNode | DNode[]) {
 			const render = renderFunc();
 			const node = findOne(render, selector);
 			node.children = node.children || [];
-			if (typeof children === 'function') {
-				children = children();
+			let childrenResult = children;
+			if (typeof childrenResult === 'function') {
+				childrenResult = childrenResult();
 			}
 			switch (type) {
 				case 'prepend':
-					node.children = [...children, ...node.children];
+					node.children = [...childrenResult, ...node.children];
 					break;
 				case 'append':
-					node.children = [...node.children, ...children];
+					node.children = [...node.children, ...childrenResult];
 					break;
 				case 'replace':
-					node.children = [...children];
+					node.children = [...childrenResult];
 					break;
 			}
 			return render;
@@ -156,7 +157,7 @@ export function assertionTemplate(renderFunc: () => DNode | DNode[]) {
 		}
 		return assertionTemplate(() => {
 			const render = renderFunc();
-			const insertedChildren = typeof children === 'function' ? (children = children()) : children;
+			const insertedChildren = typeof children === 'function' ? children() : children;
 			return replaceChildren(selector, render, (index, children) => {
 				if (type === 'after') {
 					children.splice(index + 1, 0, ...insertedChildren);

tests/testing/unit/assertionTemplate.tsx

@@ -4,7 +4,7 @@ import { stub } from 'sinon';
 
 import { harness } from '../../../src/testing/harness';
 import { WidgetBase } from '../../../src/core/WidgetBase';
-import { v, w, tsx } from '../../../src/core/vdom';
+import { v, w, tsx, create } from '../../../src/core/vdom';
 import assertionTemplate, { Ignore } from '../../../src/testing/assertionTemplate';
 
 class MyWidget extends WidgetBase<{
@@ -190,6 +190,38 @@ describe('assertionTemplate', () => {
 		h.expect(childAssertion);
 	});
 
+	it('children set should be immutable', () => {
+		const factory = create();
+		const Widget = factory(function Widget() {
+			return (
+				<div key="parent" classes={['root']}>
+					<div key="child">hello</div>
+				</div>
+			);
+		});
+
+		const WidgetWithProps = factory(function Widget() {
+			return (
+				<div key="parent" classes={['root']}>
+					<div disabled={true} key="child">
+						hello
+					</div>
+				</div>
+			);
+		});
+
+		const baseAssertion = assertionTemplate(() => v('div', { key: 'parent', classes: ['root'] }, []));
+
+		const childAssertion = baseAssertion.setChildren('@parent', () => [<div key="child">hello</div>]);
+
+		const h = harness(() => w(Widget, {}));
+		const h1 = harness(() => w(WidgetWithProps, {}));
+		h.expect(childAssertion);
+		const propertyAssertion = childAssertion.setProperty('@child', 'disabled', true);
+		h1.expect(propertyAssertion);
+		h.expect(childAssertion);
+	});
+
 	it('can set a child with replace', () => {
 		const h = harness(() => w(MyWidget, { replaceChild: true }));
 		const childAssertion = baseAssertion.replaceChildren('~header', ['replace']);