fix(amazonq): /test: show descriptive error message (aws#6795)

## Problem
Currently, when test generation fails, users see a generic error
message: `Sorry, I am experiencing technical issues at the moment.
Please try again in a few minutes.` This message doesn't provide
actionable information to help users resolve the issue.

## Solution
Enhanced error handling to display specific error messages from the
backend. For example, when a test generation command is malformed, users
will now see a descriptive message like: `I apologize, but I couldn't
process your /test instruction. Try: /test and optionally specify a
class, function or method.` These targeted error messages help users
understand and correct their inputs.



---
<img width="1722" alt="Screenshot 2025-03-17 at 10 01 53 AM"
src="https://github.com/user-attachments/assets/0f2c3279-de93-4e20-9263-cdf1eebf4603"
/>


- Treat all work as PUBLIC. Private `feature/x` branches will not be
squash-merged at release time.
- Your code changes must meet the guidelines in
[CONTRIBUTING.md](https://github.com/aws/aws-toolkit-vscode/blob/master/CONTRIBUTING.md#guidelines).
- License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

Author: chungjac

packages/amazonq/.changes/next-release/Bug Fix-7bb4ae68-204d-48a1-a510-490d2a2a938a.json

@@ -0,0 +1,4 @@
+{
+	"type": "Bug Fix",
+	"description": "/test: show descriptive error message"
+}

packages/core/src/codewhisperer/commands/startTestGeneration.ts

@@ -20,8 +20,6 @@ import { ChatSessionManager } from '../../amazonqTest/chat/storages/chatSession'
 import { ChildProcess, spawn } from 'child_process' // eslint-disable-line no-restricted-imports
 import { BuildStatus } from '../../amazonqTest/chat/session/session'
 import { fs } from '../../shared/fs/fs'
-import { TestGenerationJobStatus } from '../models/constants'
-import { TestGenFailedError } from '../../amazonqTest/error'
 import { Range } from '../client/codewhispereruserclient'
 
 // eslint-disable-next-line unicorn/no-null
@@ -112,18 +110,13 @@ export async function startTestGenerationProcess(
         if (!shouldContinueRunning(tabID)) {
             return
         }
-        const jobStatus = await pollTestJobStatus(
+        await pollTestJobStatus(
             testJob.testGenerationJob.testGenerationJobId,
             testJob.testGenerationJob.testGenerationJobGroupName,
             filePath,
             initialExecution
         )
         // TODO: Send status to test summary
-        if (jobStatus === TestGenerationJobStatus.FAILED) {
-            session.numberOfTestsGenerated = 0
-            logger.verbose(`Test generation failed.`)
-            throw new TestGenFailedError()
-        }
         throwIfCancelled()
         if (!shouldContinueRunning(tabID)) {
             return

packages/core/src/codewhisperer/service/testGenHandler.ts

@@ -18,6 +18,7 @@ import {
     CreateUploadUrlError,
     ExportResultsArchiveError,
     InvalidSourceZipError,
+    TestGenFailedError,
     TestGenStoppedError,
     TestGenTimedOutError,
 } from '../../amazonqTest/error'
@@ -193,9 +194,17 @@ export async function pollTestJobStatus(
             }
         }
         ChatSessionManager.Instance.getSession().targetFileInfo = targetFileInfo
-        if (resp.testGenerationJob?.status !== CodeWhispererConstants.TestGenerationJobStatus.IN_PROGRESS) {
-            // This can be FAILED or COMPLETED
-            status = resp.testGenerationJob?.status as CodeWhispererConstants.TestGenerationJobStatus
+        status = resp.testGenerationJob?.status as CodeWhispererConstants.TestGenerationJobStatus
+        if (status === CodeWhispererConstants.TestGenerationJobStatus.FAILED) {
+            session.numberOfTestsGenerated = 0
+            logger.verbose(`Test generation failed.`)
+            if (resp.testGenerationJob?.jobStatusReason) {
+                session.stopIteration = true
+                throw new TestGenFailedError(resp.testGenerationJob?.jobStatusReason)
+            } else {
+                throw new TestGenFailedError()
+            }
+        } else if (status === CodeWhispererConstants.TestGenerationJobStatus.COMPLETED) {
             logger.verbose(`testgen job status: ${status}`)
             logger.verbose(`Complete polling test job status.`)
             break