fix(amazonq): /test may truncate user prompt #6557

## Problem
- If user gives user input prompt more than 4096 characters, this fails
at RTS as model supports only 4096 input characters.
`Value at 'userInput' failed to satisfy constraint: Member must have
length less than or equal to 4096`
- Ideally we should not get more than 4096 char input from user input
but still features like `/test`, `/dev` were able to get the message
length more than 4096.

## Solution
- To resolve this issue, we are adding a truncation logic to continue
the test generation workflow instead of failing at RTS.
- No new tests were added as the functionality is not impacted.

Author: laileni-aws

packages/amazonq/.changes/next-release/Bug Fix-aff621e4-1c1a-450e-91a7-8fd63fe90a5d.json

@@ -0,0 +1,4 @@
+{
+	"type": "Bug Fix",
+	"description": "Amazon Q /test: Truncating user input to 4096 characters for unit test generation."
+}

packages/core/src/amazonqTest/chat/controller/controller.ts

@@ -21,6 +21,7 @@ import {
     testGenCompletedField,
     testGenProgressField,
     testGenSummaryMessage,
+    maxUserPromptLength,
 } from '../../models/constants'
 import MessengerUtils, { ButtonActions } from './messenger/messengerUtils'
 import { getTelemetryReasonDesc, isAwsError } from '../../../shared/errors'
@@ -365,7 +366,8 @@ export class TestController {
         getLogger().debug('startTestGen tabId: %O', message.tabID)
         let fileName = ''
         let filePath = ''
-        let userMessage = ''
+        let userFacingMessage = ''
+        let userPrompt = ''
         session.testGenerationStartTime = performance.now()
 
         try {
@@ -381,6 +383,8 @@ export class TestController {
                 )
                 return
             }
+            // Truncating the user prompt if the prompt is more than 4096.
+            userPrompt = message.prompt.slice(0, maxUserPromptLength)
 
             // check that the session is authenticated
             const authState = await AuthUtil.instance.getChatAuthState()
@@ -425,16 +429,16 @@ export class TestController {
             getLogger().debug(`File path: ${fileEditorToTest.document.uri.fsPath}`)
             filePath = fileEditorToTest.document.uri.fsPath
             fileName = path.basename(filePath)
-            userMessage = message.prompt
+            userFacingMessage = userPrompt
                 ? regenerateTests
-                    ? `${message.prompt}`
-                    : `/test ${message.prompt}`
+                    ? `${userPrompt}`
+                    : `/test ${userPrompt}`
                 : `/test Generate unit tests for \`${fileName}\``
 
-            session.hasUserPromptSupplied = message.prompt.length > 0
+            session.hasUserPromptSupplied = userPrompt.length > 0
 
             // displaying user message prompt in Test tab
-            this.messenger.sendMessage(userMessage, tabID, 'prompt')
+            this.messenger.sendMessage(userFacingMessage, tabID, 'prompt')
             this.messenger.sendChatInputEnabled(tabID, false)
             this.sessionStorage.getSession().conversationState = ConversationState.IN_PROGRESS
             this.messenger.sendUpdatePromptProgress(message.tabID, testGenProgressField)
@@ -460,7 +464,7 @@ export class TestController {
                 this.messenger.sendMessage(unsupportedMessage, tabID, 'answer')
                 await this.onCodeGeneration(
                     session,
-                    message.prompt,
+                    userPrompt,
                     tabID,
                     fileName,
                     filePath,

packages/core/src/amazonqTest/models/constants.ts

@@ -11,6 +11,8 @@ import { BuildStatus } from '../chat/session/session'
 // For uniquely identifiying which chat messages should be routed to Test
 export const testChat = 'testChat'
 
+export const maxUserPromptLength = 4096 // user prompt character limit from MPS and API model.
+
 export const cancelTestGenButton: ChatItemButton = {
     id: ButtonActions.STOP_TEST_GEN,
     text: 'Cancel',