diff --git a/lib/shrinkwrap.js b/lib/shrinkwrap.js
index 0dff6b2ba2bf6..33502a5601c25 100644
--- a/lib/shrinkwrap.js
+++ b/lib/shrinkwrap.js
@@ -1,14 +1,17 @@
+'use strict'
+
+const { resolve, basename } = require('path')
+const { promises: { unlink } } = require('fs')
 const Arborist = require('@npmcli/arborist')
+const log = require('npmlog')
+
 const npm = require('./npm.js')
+const completion = require('./utils/completion/none.js')
 const usageUtil = require('./utils/usage.js')
 const usage = usageUtil('shrinkwrap', 'npm shrinkwrap')
-const { resolve, basename } = require('path')
-const log = require('npmlog')
 
 const cmd = (args, cb) => shrinkwrap().then(() => cb()).catch(cb)
 
-const completion = require('./utils/completion/none.js')
-
 const shrinkwrap = async () => {
   // if has a npm-shrinkwrap.json, nothing to do
   // if has a package-lock.json, rename to npm-shrinkwrap.json
@@ -31,7 +34,6 @@ const shrinkwrap = async () => {
   const newFile = meta.hiddenLockfile || !meta.loadedFromDisk
   const oldFilename = meta.filename
   const notSW = !newFile && basename(oldFilename) !== 'npm-shrinkwrap.json'
-  const { promises: { unlink } } = require('fs')
 
   meta.hiddenLockfile = false
   meta.filename = sw
diff --git a/test/lib/shrinkwrap.js b/test/lib/shrinkwrap.js
new file mode 100644
index 0000000000000..65b16b14762d1
--- /dev/null
+++ b/test/lib/shrinkwrap.js
@@ -0,0 +1,329 @@
+const t = require('tap')
+const requireInject = require('require-inject')
+
+const npm = {
+  lockfileVersion: 2,
+  globalDir: '',
+  flatOptions: {
+    depth: 0,
+    global: false,
+  },
+  prefix: '',
+}
+const tree = {
+  meta: {
+    hiddenLockfile: null,
+    loadedFromDisk: false,
+    filename: '',
+    originalLockfileVersion: 2,
+    save () {},
+  },
+}
+const mocks = {
+  npmlog: { notice () {} },
+  '@npmcli/arborist': class {
+    loadVirtual () {
+      return tree
+    }
+
+    loadActual () {
+      return tree
+    }
+  },
+  '../../lib/npm.js': npm,
+  '../../lib/utils/usage.js': () => 'usage instructions',
+}
+
+t.afterEach(cb => {
+  npm.prefix = ''
+  npm.flatOptions.global = false
+  npm.globalDir = ''
+  cb()
+})
+
+t.test('no args', t => {
+  t.plan(4)
+
+  npm.prefix = '/project/a'
+
+  class Arborist {
+    constructor (args) {
+      t.deepEqual(
+        args,
+        { ...npm.flatOptions, path: npm.prefix },
+        'should call arborist contructor with expected args'
+      )
+    }
+
+    async loadVirtual () {
+      t.ok('should load virtual tree')
+      return {
+        ...tree,
+        meta: {
+          ...tree.meta,
+          save () {
+            t.ok('should save the lockfile')
+          },
+        },
+      }
+    }
+  }
+
+  const npmlog = {
+    notice (title, msg) {
+      t.equal(
+        msg,
+        'created a lockfile as npm-shrinkwrap.json',
+        'should log notice msg that file was successfully created'
+      )
+    },
+  }
+
+  const shrinkwrap = requireInject('../../lib/shrinkwrap.js', {
+    ...mocks,
+    npmlog,
+    '@npmcli/arborist': Arborist,
+  })
+
+  shrinkwrap([], err => {
+    if (err)
+      throw err
+  })
+})
+
+t.test('no virtual tree', t => {
+  t.plan(4)
+
+  npm.prefix = '/project/a'
+
+  class Arborist {
+    constructor (args) {
+      t.deepEqual(
+        args,
+        { ...npm.flatOptions, path: npm.prefix },
+        'should call arborist contructor with expected args'
+      )
+    }
+
+    async loadVirtual () {
+      throw new Error('ERR')
+    }
+
+    async loadActual () {
+      t.ok('should load actual tree')
+      return {
+        ...tree,
+        meta: {
+          ...tree.meta,
+          save () {
+            t.ok('should save the lockfile')
+          },
+        },
+      }
+    }
+  }
+
+  const npmlog = {
+    notice (title, msg) {
+      t.equal(
+        msg,
+        'created a lockfile as npm-shrinkwrap.json',
+        'should log notice msg that file was successfully created'
+      )
+    },
+  }
+
+  const shrinkwrap = requireInject('../../lib/shrinkwrap.js', {
+    ...mocks,
+    npmlog,
+    '@npmcli/arborist': Arborist,
+  })
+
+  shrinkwrap([], err => {
+    if (err)
+      throw err
+  })
+})
+
+t.test('existing package-json file', t => {
+  t.plan(5)
+
+  npm.prefix = '/project/a'
+
+  class Arborist {
+    constructor (args) {
+      t.deepEqual(
+        args,
+        { ...npm.flatOptions, path: npm.prefix },
+        'should call arborist contructor with expected args'
+      )
+    }
+
+    async loadVirtual () {
+      t.ok('should load virtual tree')
+      return {
+        ...tree,
+        meta: {
+          hiddenLockfile: false,
+          loadedFromDisk: true,
+          filename: 'package-lock.json',
+          save () {
+            t.ok('should save the lockfile')
+          },
+        },
+      }
+    }
+  }
+
+  const npmlog = {
+    notice (title, msg) {
+      t.equal(
+        msg,
+        'package-lock.json has been renamed to npm-shrinkwrap.json',
+        'should log notice msg that file was renamed'
+      )
+    },
+  }
+
+  const fs = {
+    promises: {
+      unlink (filename) {
+        t.equal(filename, 'package-lock.json', 'should remove old lockfile')
+      },
+    },
+  }
+
+  const shrinkwrap = requireInject('../../lib/shrinkwrap.js', {
+    ...mocks,
+    fs,
+    npmlog,
+    '@npmcli/arborist': Arborist,
+  })
+
+  shrinkwrap([], err => {
+    if (err)
+      throw err
+  })
+})
+
+t.test('update shrinkwrap file version', t => {
+  t.plan(4)
+
+  npm.prefix = '/project/a'
+
+  class Arborist {
+    constructor (args) {
+      t.deepEqual(
+        args,
+        { ...npm.flatOptions, path: npm.prefix },
+        'should call arborist contructor with expected args'
+      )
+    }
+
+    async loadVirtual () {
+      t.ok('should load virtual tree')
+      return {
+        ...tree,
+        meta: {
+          hiddenLockfile: false,
+          loadedFromDisk: true,
+          filename: 'npm-shrinkwrap.json',
+          originalLockfileVersion: 1,
+          save () {
+            t.ok('should save the lockfile')
+          },
+        },
+      }
+    }
+  }
+
+  const npmlog = {
+    notice (title, msg) {
+      t.equal(
+        msg,
+        'npm-shrinkwrap.json updated to version 2',
+        'should log notice msg that file was updated'
+      )
+    },
+  }
+
+  const shrinkwrap = requireInject('../../lib/shrinkwrap.js', {
+    ...mocks,
+    npmlog,
+    '@npmcli/arborist': Arborist,
+  })
+
+  shrinkwrap([], err => {
+    if (err)
+      throw err
+  })
+})
+
+t.test('update to date shrinkwrap file', t => {
+  t.plan(4)
+
+  npm.prefix = '/project/a'
+
+  class Arborist {
+    constructor (args) {
+      t.deepEqual(
+        args,
+        { ...npm.flatOptions, path: npm.prefix },
+        'should call arborist contructor with expected args'
+      )
+    }
+
+    async loadVirtual () {
+      t.ok('should load virtual tree')
+      return {
+        ...tree,
+        meta: {
+          hiddenLockfile: false,
+          loadedFromDisk: true,
+          filename: 'npm-shrinkwrap.json',
+          originalLockfileVersion: 2,
+          save () {
+            t.ok('should save the lockfile')
+          },
+        },
+      }
+    }
+  }
+
+  const npmlog = {
+    notice (title, msg) {
+      t.equal(
+        msg,
+        'npm-shrinkwrap.json up to date',
+        'should log notice msg shrinkwrap up to date'
+      )
+    },
+  }
+
+  const shrinkwrap = requireInject('../../lib/shrinkwrap.js', {
+    ...mocks,
+    npmlog,
+    '@npmcli/arborist': Arborist,
+  })
+
+  shrinkwrap([], err => {
+    if (err)
+      throw err
+  })
+})
+
+t.test('shrinkwrap --global', t => {
+  const shrinkwrap = requireInject('../../lib/shrinkwrap.js', mocks)
+
+  npm.flatOptions.global = true
+
+  shrinkwrap([], err => {
+    t.match(
+      err,
+      /does not work for global packages/,
+      'should throw no global support msg'
+    )
+    t.equal(err.code, 'ESHRINKWRAPGLOBAL', 'should throw expected error code')
+    t.end()
+  })
+})