diff --git a/package-lock.json b/package-lock.json
index f683580..e39ed74 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -6357,6 +6357,12 @@
       "resolved": "https://registry.npmjs.org/yallist/-/yallist-4.0.0.tgz",
       "integrity": "sha512-3wdGidZyq5PB084XLES5TpOSRA3wjXAlIWMhum2kRcv/41Sn2emQ0dycQW4uZXLejwKvg6EsvbdlVL+FYEct7A=="
     },
+    "yaml": {
+      "version": "1.10.0",
+      "resolved": "https://registry.npmjs.org/yaml/-/yaml-1.10.0.tgz",
+      "integrity": "sha512-yr2icI4glYaNG+KWONODapy2/jDdMSDnrONSjblABjD9B4Z5LgiircSt8m8sRZFNi08kG9Sm0uSHtEmP3zaEGg==",
+      "dev": true
+    },
     "yargs": {
       "version": "16.2.0",
       "resolved": "https://registry.npmjs.org/yargs/-/yargs-16.2.0.tgz",
diff --git a/package.json b/package.json
index c5182f1..6258495 100644
--- a/package.json
+++ b/package.json
@@ -77,7 +77,8 @@
     "sinon": "^9.2.2",
     "standard": "^12.0.1",
     "stream-mock": "^2.0.5",
-    "tmp": "^0.2.1"
+    "tmp": "^0.2.1",
+    "yaml": "^1.10.0"
   },
   "standard": {
     "ignore": [
diff --git a/test-fixtures/theme/album.hbs b/test-fixtures/theme/album.hbs
new file mode 100644
index 0000000..6fd504d
--- /dev/null
+++ b/test-fixtures/theme/album.hbs
@@ -0,0 +1,21 @@
+{{!--
+  This theme renders useful information as a YAML file
+  For reliable integration tests
+--}}
+
+title: {{ album.title }}
+
+albums:
+{{#each album.albums}}
+  - title: {{title}}
+    url: {{relative url}}
+{{/each}}
+
+files:
+{{#each album.files}}
+  - name: {{filename}}
+    caption: {{meta.caption}}
+    thumbnail: {{relative urls.thumbnail}}
+    preview: {{relative urls.large}}
+    download: {{relative urls.download}}
+{{/each}}
diff --git a/test-fixtures/theme/package.json b/test-fixtures/theme/package.json
new file mode 100644
index 0000000..dc3253c
--- /dev/null
+++ b/test-fixtures/theme/package.json
@@ -0,0 +1,6 @@
+{
+  "name": "@thumbsup/test-theme",
+  "thumbsup": {
+    "themeRoot": "."
+  }
+}
diff --git a/test-fixtures/theme/theme.less b/test-fixtures/theme/theme.less
new file mode 100644
index 0000000..f569c8e
--- /dev/null
+++ b/test-fixtures/theme/theme.less
@@ -0,0 +1,5 @@
+@color: #333;
+
+h1 {
+  border: @color;
+}
diff --git a/test/integration/integration-structure.spec.js b/test/integration/integration-structure.spec.js
new file mode 100644
index 0000000..8dfc24d
--- /dev/null
+++ b/test/integration/integration-structure.spec.js
@@ -0,0 +1,57 @@
+const IntegrationTest = require('./integration-test')
+const fixtures = require('../fixtures')
+
+describe('Integration: media files', function () {
+  this.slow(5000)
+  this.timeout(5000)
+
+  beforeEach(IntegrationTest.before)
+  afterEach(IntegrationTest.after)
+
+  const image = fixtures.fromDisk('photo.jpg')
+  const integration = new IntegrationTest({
+    'input/london/IMG_0001.jpg': image,
+    'input/london/IMG_0002.jpg': image,
+    'input/newyork/day 1/IMG_0003.jpg': image,
+    'input/newyork/day 2/IMG_0004.jpg': image
+  })
+
+  it('builds the gallery from scratch', function (done) {
+    const customOpts = []
+    integration.run(customOpts, () => {
+      // Database
+      integration.assertExist([
+        'thumbsup.db'
+      ])
+      // Albums
+      integration.assertExist([
+        'index.html',
+        'london.html',
+        'newyork-day-1.html',
+        'newyork-day-2.html'
+      ])
+      // Thumbnails
+      integration.assertExist([
+        'media/thumbs/london/IMG_0001.jpg',
+        'media/thumbs/london/IMG_0002.jpg',
+        'media/thumbs/newyork/day 1/IMG_0003.jpg',
+        'media/thumbs/newyork/day 2/IMG_0004.jpg'
+      ])
+      // Large versions
+      integration.assertExist([
+        'media/large/london/IMG_0001.jpg',
+        'media/large/london/IMG_0002.jpg',
+        'media/large/newyork/day 1/IMG_0003.jpg',
+        'media/large/newyork/day 2/IMG_0004.jpg'
+      ])
+      done()
+    })
+  })
+
+  it('builds the gallery a second time', function (done) {
+    const customOpts = []
+    integration.run(customOpts, () => {
+      done()
+    })
+  })
+})
diff --git a/test/integration/integration-test.js b/test/integration/integration-test.js
new file mode 100644
index 0000000..a92e111
--- /dev/null
+++ b/test/integration/integration-test.js
@@ -0,0 +1,75 @@
+const fs = require('fs')
+const debug = require('debug')
+const glob = require('glob')
+const path = require('path')
+const YAML = require('yaml')
+const should = require('should/as-function')
+const fixtures = require('../fixtures')
+const options = require('../../src/cli/options')
+const index = require('../../src/index')
+
+class IntegrationTest {
+  constructor (structure) {
+    this.tmpdir = fixtures.createTempStructure(structure)
+    this.input = path.join(this.tmpdir, 'input')
+    this.output = path.join(this.tmpdir, 'output')
+    this.actualFiles = []
+  }
+
+  run (customOptions, done) {
+    const defaultOptions = [
+      '--input', this.input,
+      '--output', this.output,
+      '--theme-path', 'test-fixtures/theme',
+      '--log', 'info'
+    ]
+    const allOptions = defaultOptions.concat(customOptions)
+    const opts = options.get(allOptions)
+    index.build(opts, err => {
+      // Reset the logger ASAP to print the test status
+      console.log = console.logOld
+      should(err).eql(null)
+      debug.assertNotContains('thumbsup:error')
+      this.actualFiles = glob.sync('**/*', {
+        cwd: this.output,
+        nodir: true,
+        nonull: false
+      })
+      setImmediate(done)
+    })
+  }
+
+  assertExist (expected) {
+    const missing = expected.filter(f => this.actualFiles.indexOf(f) === -1)
+    should(missing).eql([])
+  }
+
+  parse (filepath) {
+    const fullpath = path.join(this.output, filepath)
+    return fs.readFileSync(fullpath, { encoding: 'utf8' })
+  }
+
+  parseYaml (filepath) {
+    const contents = this.parse(filepath)
+    return YAML.parse(contents)
+  }
+
+  getPath (structurePath) {
+    return path.join(this.tmpdir, structurePath)
+  }
+}
+
+IntegrationTest.before = function () {
+  // Listr uses control.log() to print progress
+  // But so does Mocha to print test results
+  // So we override it for the duration of the integration test
+  console.logOld = console.log
+  console.log = debug('thumbsup:info')
+  debug.reset()
+}
+
+IntegrationTest.after = function () {
+  console.log = console.logOld
+}
+
+module.exports = IntegrationTest
diff --git a/test/integration/integration-themes.spec.js b/test/integration/integration-themes.spec.js
new file mode 100644
index 0000000..cf22065
--- /dev/null
+++ b/test/integration/integration-themes.spec.js
@@ -0,0 +1,38 @@
+const should = require('should/as-function')
+const IntegrationTest = require('./integration-test')
+const fixtures = require('../fixtures')
+
+describe('Integration: themes', function () {
+  this.slow(5000)
+  this.timeout(5000)
+
+  beforeEach(IntegrationTest.before)
+  afterEach(IntegrationTest.after)
+
+  const integration = new IntegrationTest({
+    'input/IMG_0001.jpg': fixtures.fromDisk('photo.jpg'),
+    'custom.less': '@color: #444;'
+  })
+
+  it('processes LESS variables', function (done) {
+    const customOpts = []
+    integration.run(customOpts, () => {
+      integration.assertExist(['public/theme.css'])
+      const res = integration.parse('public/theme.css')
+      should(res.includes('border: #333')).eql(true)
+      done()
+    })
+  })
+
+  it('can customise LESS variables', function (done) {
+    const customOpts = [
+      '--theme-style', integration.getPath('custom.less')
+    ]
+    integration.run(customOpts, () => {
+      integration.assertExist(['public/theme.css'])
+      const res = integration.parse('public/theme.css')
+      should(res.includes('border: #444')).eql(true)
+      done()
+    })
+  })
+})
diff --git a/test/integration/integration-urls.spec.js b/test/integration/integration-urls.spec.js
new file mode 100644
index 0000000..500ef65
--- /dev/null
+++ b/test/integration/integration-urls.spec.js
@@ -0,0 +1,38 @@
+const should = require('should/as-function')
+const IntegrationTest = require('./integration-test')
+const fixtures = require('../fixtures')
+
+describe('Integration: urls', function () {
+  this.slow(5000)
+  this.timeout(5000)
+
+  beforeEach(IntegrationTest.before)
+  afterEach(IntegrationTest.after)
+
+  const integration = new IntegrationTest({
+    'input/IMG_0001.jpg': fixtures.fromDisk('photo.jpg')
+  })
+
+  it('uses relative URLs by default', function (done) {
+    const customOpts = []
+    integration.run(customOpts, () => {
+      integration.assertExist(['index.html'])
+      const res = integration.parseYaml('index.html')
+      should(res.files[0].thumbnail).eql('media/thumbs/IMG_0001.jpg')
+      done()
+    })
+  })
+
+  it('can use an external link prefix', function (done) {
+    const customOpts = [
+      '--photo-preview', 'link',
+      '--link-prefix', 'http://example.com'
+    ]
+    integration.run(customOpts, () => {
+      integration.assertExist(['index.html'])
+      const res = integration.parseYaml('index.html')
+      should(res.files[0].preview).eql('http://example.com/IMG_0001.jpg')
+      done()
+    })
+  })
+})
diff --git a/test/integration/integration.spec.js b/test/integration/integration.spec.js
deleted file mode 100644
index 67ad573..0000000
--- a/test/integration/integration.spec.js
+++ /dev/null
@@ -1,107 +0,0 @@
-const debug = require('debug')
-const glob = require('glob')
-const path = require('path')
-const should = require('should/as-function')
-const fixtures = require('../fixtures')
-const options = require('../../src/cli/options')
-const index = require('../../src/index')
-
-describe('Full integration', function () {
-  this.slow(5000)
-  this.timeout(5000)
-
-  var tmpdir = null
-  var opts = null
-
-  before(() => {
-    const image = fixtures.fromDisk('photo.jpg')
-    tmpdir = fixtures.createTempStructure({
-      'input/london/IMG_0001.jpg': image,
-      'input/london/IMG_0002.jpg': image,
-      'input/newyork/day 1/IMG_0003.jpg': image,
-      'input/newyork/day 2/IMG_0004.jpg': image
-    })
-    opts = options.get([
-      '--input', path.join(tmpdir, 'input'),
-      '--output', path.join(tmpdir, 'output'),
-      '--title', 'Photo album',
-      '--homeAlbumName', 'Home',
-      '--theme', 'classic',
-      '--log', 'info'
-    ])
-  })
-
-  // Listr uses control.log() to print progress
-  // But so does Mocha to print test results
-  // So we override it for the duration of the integration test
-  beforeEach(() => {
-    console.logOld = console.log
-    console.log = debug('thumbsup:info')
-    debug.reset()
-  })
-
-  afterEach(() => {
-    console.log = console.logOld
-  })
-
-  it('builds the gallery from scratch', function (testDone) {
-    index.build(opts, err => {
-      // Reset the logger ASAP to print the test status
-      console.log = console.logOld
-      // Check for any errors
-      should(err).eql(null)
-      debug.assertNotContains('thumbsup:error')
-      // Check the contents of the output folder
-      const actualFiles = actualStructure(opts.output)
-      // Database
-      assertExist(actualFiles, [
-        'thumbsup.db'
-      ])
-      // Albums
-      assertExist(actualFiles, [
-        'index.html',
-        'london.html',
-        'newyork-day-1.html',
-        'newyork-day-2.html'
-      ])
-      // Thumbnails
-      assertExist(actualFiles, [
-        'media/thumbs/london/IMG_0001.jpg',
-        'media/thumbs/london/IMG_0002.jpg',
-        'media/thumbs/newyork/day 1/IMG_0003.jpg',
-        'media/thumbs/newyork/day 2/IMG_0004.jpg'
-      ])
-      // Large versions
-      assertExist(actualFiles, [
-        'media/large/london/IMG_0001.jpg',
-        'media/large/london/IMG_0002.jpg',
-        'media/large/newyork/day 1/IMG_0003.jpg',
-        'media/large/newyork/day 2/IMG_0004.jpg'
-      ])
-      testDone()
-    })
-  })
-
-  it('builds the gallery a second time (nothing to do)', function (testDone) {
-    index.build(opts, err => {
-      // Reset the logger ASAP to print the test status
-      console.log = console.logOld
-      should(err).eql(null)
-      testDone()
-    })
-  })
-})
-
-function actualStructure (dir) {
-  return glob.sync('**/*', {
-    cwd: dir,
-    ignore: 'public',
-    nodir: true,
-    nonull: false
-  })
-}
-
-function assertExist (actual, expected) {
-  const missing = expected.filter(f => actual.indexOf(f) === -1)
-  should([]).eql(missing)
-}