feat: allow using "new" keyword with a spy

src/spy.ts

@@ -28,9 +28,12 @@ export interface SpyImpl<A extends any[] = any[], R = any> extends Spy<A, R> {
 
 export interface SpyFn<A extends any[] = any[], R = any> extends Spy<A, R> {
   (...args: A): R
+  new (...args: A): R
 }
 
-export function spy<A extends any[], R>(cb?: (...args: A) => R): SpyFn<A, R> {
+export function spy<A extends any[], R>(
+  cb?: ((...args: A) => R) | { new (...args: A): R }
+): SpyFn<A, R> {
   assert(
     isType('function', cb) || isType('undefined', cb),
     'cannot spy on a non-function value'
@@ -100,7 +103,7 @@ export function spy<A extends any[], R>(cb?: (...args: A) => R): SpyFn<A, R> {
     fn.calls = []
   }
   reset()
-  fn.impl = cb
+  fn.impl = cb as any
   fn.reset = reset
   fn.nextError = (error: any) => {
     fn.next = ['error', error]

test/class.test.ts

@@ -30,7 +30,7 @@ describe('class mock', () => {
     expect(() => new fnArrow()).toThrowError()
   })
 
-  test('respects new.target', () => {
+  test('respects new.target in a function', () => {
     let target: unknown = null
     let args: unknown[] = []
     const fnScoped = spy(function (...fnArgs: unknown[]) {
@@ -43,4 +43,22 @@ describe('class mock', () => {
     expect(args).toEqual(['some', 'text', 1])
     expect(fnScoped.calls).toEqual([['some', 'text', 1]])
   })
+
+  test('respects new.target in a class', () => {
+    let target: unknown = null
+    let args: unknown[] = []
+    const fnScoped = spy(
+      class {
+        constructor(...fnArgs: unknown[]) {
+          target = new.target
+          args = fnArgs
+        }
+      }
+    )
+
+    new fnScoped('some', 'text', 1)
+    expect(target).toBeTypeOf('function')
+    expect(args).toEqual(['some', 'text', 1])
+    expect(fnScoped.calls).toEqual([['some', 'text', 1]])
+  })
 })