@@ -31,17 +31,8 @@ if (import.meta.url.endsWith(process.argv[1])) {
     ignoreIfLabeled: boolEnvVar('IGNORE_IF_LABELED'),
   }
 
-  // Actions pass comma-separated labels.
-  if (typeof ADD_LABELS === 'string') {
-    opts.addLabels = [...ADD_LABELS.split(',')].map((l) => l.trim())
-  } else {
-    opts.addLabels = []
-  }
-  if (typeof REMOVE_LABELS === 'string') {
-    opts.removeLabels = [...REMOVE_LABELS.split(',')].map((l) => l.trim())
-  } else {
-    opts.removeLabels = []
-  }
+  opts.addLabels = parseLabels(ADD_LABELS)
+  opts.removeLabels = parseLabels(REMOVE_LABELS)
 
   const actionContext = getActionContext()
   const { owner, repo } = actionContext
@@ -58,6 +49,14 @@ if (import.meta.url.endsWith(process.argv[1])) {
   main(coreLib, octokit, opts)
 }
 
+// Actions pass comma-separated labels, and an omitted input arrives as an empty string.
+export function parseLabels(value?: string): string[] {
+  return (value || '')
+    .split(',')
+    .map((l) => l.trim())
+    .filter(Boolean)
+}
+
 export default async function main(
   core: typeof coreLib | CoreInject,
   octokit: Octokit,
 
@@ -0,0 +1,51 @@
+import { describe, expect, test, vi } from 'vitest'
+import type { Octokit } from '@octokit/rest'
+
+import main, { parseLabels } from '../../../.github/actions/labeler/labeler'
+
+describe('parseLabels', () => {
+  test('returns no labels for a missing or empty input', () => {
+    expect(parseLabels(undefined)).toEqual([])
+    expect(parseLabels('')).toEqual([])
+  })
+
+  test('splits, trims, and drops blank labels', () => {
+    expect(parseLabels('waiting for review')).toEqual(['waiting for review'])
+    expect(parseLabels(' a, b ,')).toEqual(['a', 'b'])
+  })
+})
+
+describe('labeler main', () => {
+  test('does not add labels when the addLabels input is empty', async () => {
+    const addLabels = vi.fn()
+    const removeLabel = vi.fn()
+    const octokit = {
+      issues: {
+        get: vi.fn().mockResolvedValue({ data: { labels: [{ name: 'waiting for review' }] } }),
+        addLabels,
+        removeLabel,
+      },
+    } as unknown as Octokit
+    const core = {
+      info: vi.fn(),
+      debug: vi.fn(),
+      warning: vi.fn(),
+      error: vi.fn(),
+      setOutput: vi.fn(),
+      setFailed: vi.fn(),
+    }
+
+    await main(core, octokit, {
+      addLabels: parseLabels(''),
+      removeLabels: parseLabels('waiting for review'),
+      issue_number: 1,
+      owner: 'github',
+      repo: 'docs',
+    })
+
+    expect(removeLabel).toHaveBeenCalledWith(
+      expect.objectContaining({ name: 'waiting for review' }),
+    )
+    expect(addLabels).not.toHaveBeenCalled()
+  })
+})