diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 4a98fec..7b734fc 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -13,5 +13,8 @@ jobs:
           timezoneLinux: 'Asia/Tokyo'
       - uses: actions/checkout@v4
       - uses: ./.github/actions/prepare
+      - name: Create .env file
+        run: |
+          echo "OPENAI_API_KEY=${{ secrets.OPENAI_API_KEY }}" > .env
       - name: Test
         run: pnpm test
diff --git a/test/commit-message-fixtures.test.js b/test/commit-message-fixtures.test.js
new file mode 100644
index 0000000..1794814
--- /dev/null
+++ b/test/commit-message-fixtures.test.js
@@ -0,0 +1,131 @@
+import { describe, it, expect, beforeEach } from 'vitest'
+import { validateTestFixtureCommitMessage } from '../utils/validateTestFixtureCommitMessage'
+import * as path from 'path'
+import * as fs from 'fs'
+import OpenAI from 'openai'
+import dotenv from 'dotenv'
+
+dotenv.config()
+
+const openai = new OpenAI({ apiKey: process.env.OPENAI_API_KEY })
+
+describe('Test Fixture Commit Message Validation', () => {
+  beforeEach(() => {})
+
+  it('should validate commit messages when test fixture files are modified', async () => {
+    if (!process.env.OPENAI_API_KEY) {
+      console.warn('Skipping test: No OpenAI API key available')
+      return
+    }
+
+    const testFixtureDiff = `
+diff --git a/test/fixtures/array/chunk.js b/test/fixtures/array/chunk.js
+index 1234567..abcdefg 100644
+--- a/test/fixtures/array/chunk.js
++++ b/test/fixtures/array/chunk.js
+@@ -1,5 +1,6 @@
+ /**
+- * Creates an array of elements split into groups the length of size.
++ * Creates an array of elements split into groups the length of size.
++ * If array can't be split evenly, the final chunk will be the remaining elements.
+  *
+  * @param {Array} array - The array to process
+  * @param {number} [size=1] - The length of each chunk
+`
+
+    const messages = [
+      {
+        role: 'system',
+        content:
+          'You are a helpful assistant. Write the commit message in English. This commit modifies test fixtures, so begin your message with "test:" and include "update fixture for [functionality]".',
+      },
+      {
+        role: 'user',
+        content: `Generate a Git commit message based on the following summary: ${testFixtureDiff}\n\nCommit message: `,
+      },
+    ]
+
+    const parameters = {
+      model: 'gpt-4o',
+      messages,
+      n: 1,
+      temperature: 0,
+      max_tokens: 50,
+    }
+
+    const response = await openai.chat.completions.create(parameters)
+    const message = response.choices[0].message.content.trim()
+
+    const isValidCommitMessage = validateTestFixtureCommitMessage(
+      message,
+      'array',
+    )
+
+    expect(isValidCommitMessage).toBe(true)
+  })
+
+  it('should reject invalid commit messages for fixture changes', async () => {
+    if (!process.env.OPENAI_API_KEY) {
+      console.warn('Skipping test: No OpenAI API key available')
+      return
+    }
+
+    const testFixtureDiff = `
+diff --git a/test/fixtures/string/camelCase.js b/test/fixtures/string/camelCase.js
+index 1234567..abcdefg 100644
+--- a/test/fixtures/string/camelCase.js
++++ b/test/fixtures/string/camelCase.js
+@@ -1,4 +1,5 @@
+ /**
++ * Improved documentation.
+  * Converts string to camel case.
+  *
+  * @param {string} string - The string to convert
+`
+
+    const messages = [
+      {
+        role: 'system',
+        content:
+          'You are a helpful assistant. Write the commit message in English. This is a bugfix, so begin your message with "fix:".',
+      },
+      {
+        role: 'user',
+        content: `Generate a Git commit message based on the following summary: ${testFixtureDiff}\n\nCommit message: `,
+      },
+    ]
+
+    const parameters = {
+      model: 'gpt-4o',
+      messages,
+      n: 1,
+      temperature: 0,
+      max_tokens: 50,
+    }
+
+    const response = await openai.chat.completions.create(parameters)
+    const message = response.choices[0].message.content.trim()
+
+    const isValidCommitMessage = validateTestFixtureCommitMessage(
+      message,
+      'string',
+    )
+
+    expect(isValidCommitMessage).toBe(false)
+  })
+
+  it('should recognize test fixture directory changes', () => {
+    const fixturesPath = path.join(process.cwd(), 'test', 'fixtures')
+    const exists = fs.existsSync(fixturesPath)
+
+    expect(exists).toBe(true)
+
+    const arrayDirExists = fs.existsSync(path.join(fixturesPath, 'array'))
+    const objectDirExists = fs.existsSync(path.join(fixturesPath, 'object'))
+    const stringDirExists = fs.existsSync(path.join(fixturesPath, 'string'))
+
+    expect(arrayDirExists).toBe(true)
+    expect(objectDirExists).toBe(true)
+    expect(stringDirExists).toBe(true)
+  })
+})
diff --git a/test/fixtures/array/chunk.js b/test/fixtures/array/chunk.js
new file mode 100644
index 0000000..503fff1
--- /dev/null
+++ b/test/fixtures/array/chunk.js
@@ -0,0 +1,23 @@
+/**
+ * Creates an array of elements split into groups the length of size.
+ * If array can't be split evenly, the final chunk will be the remaining elements.
+ *
+ * @param {Array} array - The array to process
+ * @param {number} [size=1] - The length of each chunk
+ * @returns {Array} Returns the new array of chunks
+ */
+export function chunk(array, size = 1) {
+  const length = array == null ? 0 : array.length
+  if (!length || size < 1) {
+    return []
+  }
+
+  const result = []
+  let index = 0
+
+  while (index < length) {
+    result.push(array.slice(index, (index += size)))
+  }
+
+  return result
+}
diff --git a/test/fixtures/object/pick.js b/test/fixtures/object/pick.js
new file mode 100644
index 0000000..ba747a7
--- /dev/null
+++ b/test/fixtures/object/pick.js
@@ -0,0 +1,24 @@
+/**
+ * Creates an object composed of the picked object properties.
+ *
+ * @param {Object} object - The source object
+ * @param {...(string|string[])} [paths] - The property paths to pick
+ * @returns {Object} Returns the new object
+ */
+export function pick(object, ...paths) {
+  const result = {}
+
+  if (object == null) {
+    return result
+  }
+
+  const flatPaths = [].concat(...paths)
+
+  flatPaths.forEach((path) => {
+    if (path in object) {
+      result[path] = object[path]
+    }
+  })
+
+  return result
+}
diff --git a/test/fixtures/string/camelCase.js b/test/fixtures/string/camelCase.js
new file mode 100644
index 0000000..8576285
--- /dev/null
+++ b/test/fixtures/string/camelCase.js
@@ -0,0 +1,15 @@
+/**
+ * Converts string to camel case.
+ *
+ * @param {string} string - The string to convert
+ * @returns {string} Returns the camel cased string
+ */
+export function camelCase(string) {
+  if (!string) {
+    return ''
+  }
+
+  return string
+    .replace(/[^a-zA-Z0-9]+(.)/g, (_, chr) => chr.toUpperCase())
+    .replace(/^[A-Z]/, (c) => c.toLowerCase())
+}
diff --git a/utils/validateTestFixtureCommitMessage.js b/utils/validateTestFixtureCommitMessage.js
new file mode 100644
index 0000000..30bbba3
--- /dev/null
+++ b/utils/validateTestFixtureCommitMessage.js
@@ -0,0 +1,33 @@
+/**
+ * Validates that commit messages for test fixture changes follow the required format
+ * Format: "test: update fixture for [functionality]"
+ *
+ * @param {string} message - The commit message to validate
+ * @param {string} [fixtureType] - Optional fixture type to validate against
+ * @returns {boolean} Returns true if the message is valid, false otherwise
+ */
+export function validateTestFixtureCommitMessage(message, fixtureType = null) {
+  if (!message) {
+    return false
+  }
+
+  const basicFormatRegex = /^test(\(fixtures\))?:/i
+  if (!basicFormatRegex.test(message)) {
+    return false
+  }
+
+  const updateFixtureRegex =
+    /update fixture|add fixture|modify fixture|fixture change/i
+  if (!updateFixtureRegex.test(message)) {
+    return false
+  }
+
+  if (
+    fixtureType &&
+    !message.toLowerCase().includes(fixtureType.toLowerCase())
+  ) {
+    return false
+  }
+
+  return true
+}
diff --git a/utils/validateTestFixtureCommitMessage.test.js b/utils/validateTestFixtureCommitMessage.test.js
new file mode 100644
index 0000000..76ad842
--- /dev/null
+++ b/utils/validateTestFixtureCommitMessage.test.js
@@ -0,0 +1,53 @@
+import { describe, it, expect } from 'vitest'
+import { validateTestFixtureCommitMessage } from './validateTestFixtureCommitMessage'
+
+describe('validateTestFixtureCommitMessage', () => {
+  it('should return false for an empty commit message', () => {
+    expect(validateTestFixtureCommitMessage('')).toBe(false)
+  })
+
+  it('should return true for valid test fixture commit messages', () => {
+    expect(
+      validateTestFixtureCommitMessage(
+        'test: update fixture for array methods',
+      ),
+    ).toBe(true)
+    expect(
+      validateTestFixtureCommitMessage(
+        'test(fixtures): add fixture for object utility',
+      ),
+    ).toBe(true)
+    expect(
+      validateTestFixtureCommitMessage(
+        'test: modify fixture for string camelCase',
+      ),
+    ).toBe(true)
+  })
+
+  it('should return false for invalid test fixture commit messages', () => {
+    expect(validateTestFixtureCommitMessage('feat: add new feature')).toBe(
+      false,
+    )
+    expect(validateTestFixtureCommitMessage('fix: update test fixture')).toBe(
+      false,
+    )
+    expect(validateTestFixtureCommitMessage('test: fix bug in main code')).toBe(
+      false,
+    )
+  })
+
+  it('should validate specific fixture types if provided', () => {
+    expect(
+      validateTestFixtureCommitMessage(
+        'test: update fixture for array methods',
+        'array',
+      ),
+    ).toBe(true)
+    expect(
+      validateTestFixtureCommitMessage(
+        'test: update fixture for string methods',
+        'array',
+      ),
+    ).toBe(false)
+  })
+})