fix: mockImplementation doesn't clear once stack

__test__/jest/mock.test.js

@@ -14,6 +14,21 @@ test('methods are overridable', () => {
   expect(f()).toBe(1)
 })
 
+test('mockImplementationOnce stacks and takes precedence even when is called before', () => {
+  const f = jest.fn(() => 2)
+  expect(f()).toBe(2)
+  expect(f()).toBe(2)
+  f.mockImplementationOnce(() => 4)
+  f.mockImplementationOnce(() => 5)
+  expect(f()).toBe(4)
+  f.mockImplementationOnce(() => 6)
+  f.mockImplementation(() => 3)
+  expect(f()).toBe(5)
+  expect(f()).toBe(6)
+  expect(f()).toBe(3)
+  expect(f()).toBe(3)
+})
+
 test('mockReset resets to undefined', () => {
   const f = jest.fn(() => 1)
   expect(f()).toBe(1)

src/jest.fn.js

@@ -61,7 +61,6 @@ export const jestfn = (baseimpl, parent, property) => {
 
   const queuedMock = (impl) => {
     mockimpl = impl || noop
-    onceStack.length = 0
   }
 
   // getMockImplementation() is undocumented and is changed only in real mockImplementation() call