Added reduce() function for FindWrapper

index.d.ts

@@ -38,6 +38,11 @@ export interface FindWrapper<P, S> {
      **/
     find<Q, T>(selector: string): FindWrapper<Q, T>;
 
+    /**
+     * Applies provided function to every element, returning a single value.
+     **/
+    reduce<T>(fn: (prevVal: T, wrapper: this, index: number) => T, initialValue: T): T;
+
     /** Requires a single `Component` or functional node. Returns the raw vdom output of the given component. */
     output(): preact.VNode;
 
@@ -84,4 +89,4 @@ interface ShallowFunction {
 export const deep: DeepFunction;
 export const render: DeepFunction;
 export const shallow: ShallowFunction;
-export default deep;
+export default deep;

src/preact-render-spy.js

@@ -270,6 +270,17 @@ class FindWrapper {
     );
   }
 
+  reduce(fn, initialValue) {
+    verifyFoundNodes(this);
+    if (initialValue === undefined) {
+      throw new Error('preact-render-spy: reduce initialValue is missing');
+    }
+    return Array.from(this).reduce(
+      (accumulator, vnode, index) => fn(accumulator, new FindWrapper(this.context, [vnode]), index),
+      initialValue
+    );
+  }
+
   component() {
     if (this.length !== 1) {
       throw new Error('preact-render-spy: component method can only be used on a single node');

src/shared-render.test.js

@@ -171,6 +171,12 @@ const sharedTests = (name, func) => {
     expect(context.filter(<span />).length).toBe(0);
   });
 
+  it(`${name}: reduce components`, () => {
+    const context = func(<div><NullStateless class="first" value={1} /><NullStateless value={2} /></div>);
+    expect(context.find('NullStateless').reduce((sum, n) => sum + n.attr('value'), 1)).toEqual(4);
+    expect(() => context.find('NullStateless').reduce((sum, n) => sum + n.attr('value'))).toThrow();
+  });
+
   it(`${name}: output returns vdom output by a Component`, () => {
     const context = func(<DivChildren><span /></DivChildren>);
     expect(() => context.find('div').output()).toThrow();