diff --git a/src/__tests__/validate-plugin.js b/src/__tests__/validate-plugin.js
index 725ece8b..5ebdf409 100644
--- a/src/__tests__/validate-plugin.js
+++ b/src/__tests__/validate-plugin.js
@@ -16,7 +16,7 @@ test('can validate using plugin', async () => {
   )
 
   // Assert error messages are not in the DOM when rendering the component.
-  expect(queryByTestId('username-errors')).toBeNull()
+  expect(queryByTestId('username-errors')).not.toBeInTheDocument()
 
   const usernameInput = getByPlaceholderText('Username...')
   await fireEvent.touch(usernameInput)
diff --git a/src/__tests__/vue-i18n.js b/src/__tests__/vue-i18n.js
index 45f2ba7e..381a2736 100644
--- a/src/__tests__/vue-i18n.js
+++ b/src/__tests__/vue-i18n.js
@@ -36,5 +36,5 @@ test('renders translations', async () => {
 
   expect(getByText('こんにちは')).toBeInTheDocument()
 
-  expect(queryByText('Hello')).toBeNull()
+  expect(queryByText('Hello')).not.toBeInTheDocument()
 })
diff --git a/types/index.d.ts b/types/index.d.ts
index d7da0690..cedc5340 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -46,12 +46,16 @@ export interface RenderOptions<V extends Vue, S = {}>
   baseElement?: Element
 }
 
-export type ConfigurationCallback<V extends Vue> = (
+type ConfigurationArgs = [
   localVue: typeof Vue,
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   store: Store<any>,
   router: Router,
-) => Partial<ThisTypedMountOptions<V>> | void
+]
+
+export type ConfigurationCallback<V extends Vue> =
+  | ((...args: ConfigurationArgs) => Partial<ThisTypedMountOptions<V>>)
+  | ((...args: ConfigurationArgs) => void)
 
 export function render<V extends Vue>(
   TestComponent: VueClass<V> | ComponentOptions<V>,