diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e48b7a9..b283421 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,26 +1,31 @@
 name: CI
 on: push
 jobs:
-  lint:
+  test:
+    name: Unit tests
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: goto-bus-stop/standard-action@v1
-        with:
-          annotate: true
-        env:
-          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
+      - name: Checkout sources
+        uses: actions/checkout@v2
+      - name: Install dependencies
+        run: npm install
+      - name: Run tests
+        run: npm test
 
   smoke-test:
+    name: Build test
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
         zig-version: [0.5.0, master]
     runs-on: ${{matrix.os}}
     steps:
-      - uses: actions/checkout@v2
-      - uses: goto-bus-stop/setup-zig@default
+      - name: Checkout sources
+        uses: actions/checkout@v2
+      - name: Install Zig
+        uses: goto-bus-stop/setup-zig@default
         with:
           version: ${{matrix.zig-version}}
-      - run: zig build test
+      - name: Run tests
+        run: zig build test
         working-directory: test
diff --git a/index.js b/index.js
index 8cd4b09..b1753a2 100644
--- a/index.js
+++ b/index.js
@@ -1,69 +1,13 @@
 const os = require('os')
 const path = require('path')
 const semver = require('semver')
-const get = require('simple-get').concat
 const actions = require('@actions/core')
 const cache = require('@actions/tool-cache')
-
-function getJSON (opts) {
-  return new Promise((resolve, reject) => {
-    get({ ...opts, json: true }, (err, req, data) => {
-      if (err) {
-        reject(err)
-      } else {
-        resolve(data)
-      }
-    })
-  })
-}
-
-function extForPlatform (platform) {
-  return {
-    linux: 'tar.xz',
-    darwin: 'tar.xz',
-    win32: 'zip'
-  }[platform]
-}
-
-function resolveCommit (platform, version) {
-  const ext = extForPlatform(platform)
-  const addrhost = {
-    linux: 'linux-x86_64',
-    darwin: 'macos-x86_64',
-    win32: 'windows-x86_64'
-  }[platform]
-
-  const downloadUrl = `https://ziglang.org/builds/zig-${addrhost}-${version}.${ext}`
-  const variantName = `zig-${addrhost}-${version}`
-
-  return { downloadUrl, variantName }
-}
-
-async function resolveVersion (platform, version) {
-  const ext = extForPlatform(platform)
-  const host = {
-    linux: 'x86_64-linux',
-    darwin: 'x86_64-macos',
-    win32: 'x86_64-windows'
-  }[platform] || platform
-
-  const index = await getJSON({ url: 'https://ziglang.org/download/index.json' })
-
-  const availableVersions = Object.keys(index)
-  const useVersion = semver.valid(version)
-    ? semver.maxSatisfying(availableVersions.filter((v) => semver.valid(v)), version)
-    : null
-
-  const meta = index[useVersion || version]
-  if (!meta || !meta[host]) {
-    throw new Error(`Could not find version ${version} for platform ${host}`)
-  }
-
-  const downloadUrl = meta[host].tarball
-  const variantName = path.basename(meta[host].tarball).replace(`.${ext}`, '')
-
-  return { downloadUrl, variantName }
-}
+const {
+  extForPlatform,
+  resolveCommit,
+  resolveVersion
+} = require('./versions')
 
 async function downloadZig (platform, version) {
   const ext = extForPlatform(platform)
diff --git a/package.json b/package.json
index cf09137..c22a8e4 100644
--- a/package.json
+++ b/package.json
@@ -31,7 +31,7 @@
   },
   "scripts": {
     "prepare": "ncc build index.js -o dist",
-    "test": "standard"
+    "test": "standard && node test"
   },
   "standard": {
     "ignore": [
diff --git a/test.js b/test.js
new file mode 100644
index 0000000..3860a28
--- /dev/null
+++ b/test.js
@@ -0,0 +1,32 @@
+const assert = require('assert').strict
+const {
+  resolveCommit,
+  resolveVersion
+} = require('./versions')
+
+async function test () {
+  assert.deepEqual(resolveCommit('linux', '0.6.0+4b48fccad'), {
+    downloadUrl: 'https://ziglang.org/builds/zig-linux-x86_64-0.6.0+4b48fccad.tar.xz',
+    variantName: 'zig-linux-x86_64-0.6.0+4b48fccad'
+  })
+  assert.deepEqual(resolveCommit('win32', '0.6.0+4b48fccad'), {
+    downloadUrl: 'https://ziglang.org/builds/zig-windows-x86_64-0.6.0+4b48fccad.zip',
+    variantName: 'zig-windows-x86_64-0.6.0+4b48fccad'
+  })
+
+  assert.deepEqual(await resolveVersion('linux', '0.7.0'), {
+    downloadUrl: 'https://ziglang.org/download/0.7.0/zig-linux-x86_64-0.7.0.tar.xz',
+    variantName: 'zig-linux-x86_64-0.7.0'
+  })
+  assert.deepEqual(await resolveVersion('win32', '0.4.0'), {
+    downloadUrl: 'https://ziglang.org/download/0.4.0/zig-windows-x86_64-0.4.0.zip',
+    variantName: 'zig-windows-x86_64-0.4.0'
+  })
+  await assert.doesNotReject(resolveVersion('linux', 'master'))
+  await assert.doesNotReject(resolveVersion('win32', 'master'))
+}
+
+test().catch((error) => {
+  console.error(error.stack)
+  process.exit(1)
+})
diff --git a/versions.js b/versions.js
new file mode 100644
index 0000000..cd08c4f
--- /dev/null
+++ b/versions.js
@@ -0,0 +1,69 @@
+const path = require('path')
+const get = require('simple-get').concat
+const semver = require('semver')
+
+function extForPlatform (platform) {
+  return {
+    linux: 'tar.xz',
+    darwin: 'tar.xz',
+    win32: 'zip'
+  }[platform]
+}
+
+function resolveCommit (platform, version) {
+  const ext = extForPlatform(platform)
+  const addrhost = {
+    linux: 'linux-x86_64',
+    darwin: 'macos-x86_64',
+    win32: 'windows-x86_64'
+  }[platform]
+
+  const downloadUrl = `https://ziglang.org/builds/zig-${addrhost}-${version}.${ext}`
+  const variantName = `zig-${addrhost}-${version}`
+
+  return { downloadUrl, variantName }
+}
+
+function getJSON (opts) {
+  return new Promise((resolve, reject) => {
+    get({ ...opts, json: true }, (err, req, data) => {
+      if (err) {
+        reject(err)
+      } else {
+        resolve(data)
+      }
+    })
+  })
+}
+
+async function resolveVersion (platform, version) {
+  const ext = extForPlatform(platform)
+  const host = {
+    linux: 'x86_64-linux',
+    darwin: 'x86_64-macos',
+    win32: 'x86_64-windows'
+  }[platform] || platform
+
+  const index = await getJSON({ url: 'https://ziglang.org/download/index.json' })
+
+  const availableVersions = Object.keys(index)
+  const useVersion = semver.valid(version)
+    ? semver.maxSatisfying(availableVersions.filter((v) => semver.valid(v)), version)
+    : null
+
+  const meta = index[useVersion || version]
+  if (!meta || !meta[host]) {
+    throw new Error(`Could not find version ${useVersion || version} for platform ${host}`)
+  }
+
+  const downloadUrl = meta[host].tarball
+  const variantName = path.basename(meta[host].tarball).replace(`.${ext}`, '')
+
+  return { downloadUrl, variantName }
+}
+
+module.exports = {
+  extForPlatform,
+  resolveCommit,
+  resolveVersion
+}