tests(CodeWhisperer): add accountless unit test case (#2731)

## Problem

There are no unit tests for `showAccessTokenPrompt`
`showAccessTokenPrompt` is implemented as a combination of a quick pick and input box. It's meant to be temporary.

## Solution

Add basic test cases

Author: gmeghrao

src/test/codewhisperer/util/showAccessTokenPrompt.test.ts

@@ -0,0 +1,75 @@
+/*!
+ * Copyright 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as assert from 'assert'
+import * as sinon from 'sinon'
+import * as vscode from 'vscode'
+import { DefaultCodeWhispererClient } from '../../../codewhisperer/client/codewhisperer'
+import { exposeEmitters } from '../../shared/vscode/testUtils'
+import { showAccessTokenPrompt } from '../../../codewhisperer/util/showAccessTokenPrompt'
+import { sleep } from '../../../shared/utilities/timeoutUtils'
+
+function stubQuickInputs() {
+    const picker = exposeEmitters(vscode.window.createQuickPick(), ['onDidAccept', 'onDidChangeValue'])
+
+    const inputBox = exposeEmitters(vscode.window.createInputBox(), ['onDidAccept', 'onDidChangeValue'])
+    sinon.stub(vscode.window, 'createQuickPick').returns(picker)
+    sinon.stub(vscode.window, 'createInputBox').returns(inputBox)
+
+    return { picker, inputBox }
+}
+
+describe('showAccessTokenPrompt', function () {
+    afterEach(function () {
+        sinon.restore()
+    })
+
+    it('shows an error message when the backend rejects the user input', async function () {
+        const mockClient: DefaultCodeWhispererClient = new DefaultCodeWhispererClient()
+        const { picker, inputBox } = stubQuickInputs()
+        sinon.stub(mockClient, 'getAccessToken').rejects(new Error('Invalid access code. Please re-enter.'))
+
+        showAccessTokenPrompt(mockClient, () => {})
+
+        picker.value = 'bad input'
+        picker.fireOnDidAccept()
+
+        await sleep()
+        assert.strictEqual(inputBox.validationMessage, 'Invalid access code. Please re-enter.')
+    })
+
+    it('shows an error message for empty user input', async function () {
+        const mockClient: DefaultCodeWhispererClient = new DefaultCodeWhispererClient()
+        const { picker, inputBox } = stubQuickInputs()
+        sinon.stub(mockClient, 'getAccessToken').rejects(new Error('Invalid access code. Please re-enter.'))
+
+        showAccessTokenPrompt(mockClient, () => {})
+
+        picker.value = ''
+        picker.fireOnDidAccept()
+
+        await sleep()
+        assert.strictEqual(inputBox.validationMessage, 'Invalid access code. Please re-enter.')
+    })
+
+    it('executes the callback parameter for valid user input', async function () {
+        let out
+        const setToken = (token: string) => {
+            out = token
+        }
+        const mockClient: DefaultCodeWhispererClient = new DefaultCodeWhispererClient()
+        const mockServerResult = {
+            accessToken: 'token',
+        }
+        const { picker } = stubQuickInputs()
+        sinon.stub(mockClient, 'getAccessToken').resolves(mockServerResult)
+        showAccessTokenPrompt(mockClient, setToken)
+        picker.value = 'token'
+        picker.fireOnDidAccept()
+
+        await sleep()
+        assert.strictEqual(picker.value, out)
+    })
+})