diff --git a/tests/helpers/fixtures.py b/tests/helpers/fixtures.py
index a01c72788..6e17ebd71 100644
--- a/tests/helpers/fixtures.py
+++ b/tests/helpers/fixtures.py
@@ -37,13 +37,14 @@ import pytest
 import py.path  # pylint: disable=no-name-in-module
 
 import helpers.stubs as stubsmod
+import helpers.utils
 from qutebrowser.config import config, configdata, configtypes, configexc
 from qutebrowser.utils import objreg, standarddir
 from qutebrowser.browser.webkit import cookies
 from qutebrowser.misc import savemanager, sql
 from qutebrowser.keyinput import modeman
 
-from PyQt5.QtCore import pyqtSignal, QEvent, QSize, Qt, QObject
+from PyQt5.QtCore import QEvent, QSize, Qt
 from PyQt5.QtGui import QKeyEvent
 from PyQt5.QtWidgets import QWidget, QHBoxLayout, QVBoxLayout
 from PyQt5.QtNetwork import QNetworkCookieJar
@@ -78,34 +79,9 @@ class WinRegistryHelper:
             del objreg.window_registry[win_id]
 
 
-class CallbackChecker(QObject):
-
-    """Check if a value provided by a callback is the expected one."""
-
-    got_result = pyqtSignal(object)
-    UNSET = object()
-
-    def __init__(self, qtbot, parent=None):
-        super().__init__(parent)
-        self._qtbot = qtbot
-        self._result = self.UNSET
-
-    def callback(self, result):
-        """Callback which can be passed to runJavaScript."""
-        self._result = result
-        self.got_result.emit(result)
-
-    def check(self, expected):
-        """Wait until the JS result arrived and compare it."""
-        if self._result is self.UNSET:
-            with self._qtbot.waitSignal(self.got_result, timeout=2000):
-                pass
-        assert self._result == expected
-
-
 @pytest.fixture
 def callback_checker(qtbot):
-    return CallbackChecker(qtbot)
+    return helpers.utils.CallbackChecker(qtbot)
 
 
 class FakeStatusBar(QWidget):
diff --git a/tests/helpers/utils.py b/tests/helpers/utils.py
index e6e3d37c8..82c07fbd2 100644
--- a/tests/helpers/utils.py
+++ b/tests/helpers/utils.py
@@ -27,6 +27,8 @@ import contextlib
 
 import pytest
 
+from PyQt5.QtCore import QObject, pyqtSignal
+
 from qutebrowser.utils import qtutils
 
 
@@ -176,3 +178,28 @@ def abs_datapath():
 @contextlib.contextmanager
 def nop_contextmanager():
     yield
+
+
+class CallbackChecker(QObject):
+
+    """Check if a value provided by a callback is the expected one."""
+
+    got_result = pyqtSignal(object)
+    UNSET = object()
+
+    def __init__(self, qtbot, parent=None):
+        super().__init__(parent)
+        self._qtbot = qtbot
+        self._result = self.UNSET
+
+    def callback(self, result):
+        """Callback which can be passed to runJavaScript."""
+        self._result = result
+        self.got_result.emit(result)
+
+    def check(self, expected):
+        """Wait until the JS result arrived and compare it."""
+        if self._result is self.UNSET:
+            with self._qtbot.waitSignal(self.got_result, timeout=2000):
+                pass
+        assert self._result == expected
diff --git a/tests/unit/javascript/conftest.py b/tests/unit/javascript/conftest.py
index b9f013ecf..8490a5362 100644
--- a/tests/unit/javascript/conftest.py
+++ b/tests/unit/javascript/conftest.py
@@ -26,6 +26,12 @@ import logging
 import pytest
 import jinja2
 
+from PyQt5.QtCore import QUrl
+
+import helpers.utils
+import qutebrowser.utils.debug
+from qutebrowser.utils import utils
+
 try:
     from PyQt5.QtWebKit import QWebSettings
     from PyQt5.QtWebKitWidgets import QWebPage
@@ -34,7 +40,14 @@ except ImportError:
     QWebSettings = None
     QWebPage = None
 
-from qutebrowser.utils import utils
+try:
+    from PyQt5.QtWebEngineWidgets import (QWebEnginePage,
+                                          QWebEngineSettings,
+                                          QWebEngineScript)
+except ImportError:
+    QWebEnginePage = None
+    QWebEngineSettings = None
+    QWebEngineScript = None
 
 
 if QWebPage is None:
@@ -68,9 +81,96 @@ else:
             """Fail tests on js console messages as they're used for errors."""
             pytest.fail("js console ({}:{}): {}".format(source, line, msg))
 
+if QWebEnginePage is None:
+    TestWebEnginePage = None
+else:
+    class TestWebEnginePage(QWebEnginePage):
+
+        """QWebEnginePage which overrides javascript logging methods.
+
+        Attributes:
+            _logger: The logger used for alerts.
+        """
+
+        def __init__(self, parent=None):
+            super().__init__(parent)
+            self._logger = logging.getLogger('js-tests')
+
+        def javaScriptAlert(self, _frame, msg):
+            """Log javascript alerts."""
+            self._logger.info("js alert: {}".format(msg))
+
+        def javaScriptConfirm(self, _frame, msg):
+            """Fail tests on js confirm() as that should never happen."""
+            pytest.fail("js confirm: {}".format(msg))
+
+        def javaScriptPrompt(self, _frame, msg, _default):
+            """Fail tests on js prompt() as that should never happen."""
+            pytest.fail("js prompt: {}".format(msg))
+
+        def javaScriptConsoleMessage(self, level, msg, line, source):
+            """Fail tests on js console messages as they're used for errors."""
+            pytest.fail("[{}] js console ({}:{}): {}".format(
+                qutebrowser.utils.debug.qenum_key(
+                    QWebEnginePage, level), source, line, msg))
+
 
 class JSTester:
 
+    """Common subclass providing basic functionality for all JS testers.
+
+    Attributes:
+        webview: The webview which is used.
+        _qtbot: The QtBot fixture from pytest-qt.
+        _jinja_env: The jinja2 environment used to get templates.
+    """
+
+    def __init__(self, webview, qtbot):
+        self.webview = webview
+        self._qtbot = qtbot
+        loader = jinja2.FileSystemLoader(os.path.dirname(__file__))
+        self._jinja_env = jinja2.Environment(loader=loader, autoescape=True)
+
+    def load(self, path, **kwargs):
+        """Load and display the given jinja test data.
+
+        Args:
+            path: The path to the test file, relative to the javascript/
+                  folder.
+            **kwargs: Passed to jinja's template.render().
+        """
+        template = self._jinja_env.get_template(path)
+        with self._qtbot.waitSignal(self.webview.loadFinished,
+                                    timeout=2000) as blocker:
+            self.webview.setHtml(template.render(**kwargs))
+        assert blocker.args == [True]
+
+    def load_file(self, path: str, force: bool = False):
+        """Load a file from disk.
+
+        Args:
+            path: The string path from disk to load (relative to this file)
+            force: Whether to force loading even if the file is invalid.
+        """
+        self.load_url(QUrl.fromLocalFile(
+            os.path.join(os.path.dirname(__file__), path)), force)
+
+    def load_url(self, url: QUrl, force: bool = False):
+        """Load a given QUrl.
+
+        Args:
+            url: The QUrl to load.
+            force: Whether to force loading even if the file is invalid.
+        """
+        with self._qtbot.waitSignal(self.webview.loadFinished,
+                                    timeout=2000) as blocker:
+            self.webview.load(url)
+        if not force:
+            assert blocker.args == [True]
+
+
+class JSWebKitTester(JSTester):
+
     """Object returned by js_tester which provides test data and a webview.
 
     Attributes:
@@ -80,11 +180,8 @@ class JSTester:
     """
 
     def __init__(self, webview, qtbot):
-        self.webview = webview
+        super().__init__(webview, qtbot)
         self.webview.setPage(TestWebPage(self.webview))
-        self._qtbot = qtbot
-        loader = jinja2.FileSystemLoader(os.path.dirname(__file__))
-        self._jinja_env = jinja2.Environment(loader=loader, autoescape=True)
 
     def scroll_anchor(self, name):
         """Scroll the main frame to the given anchor."""
@@ -94,19 +191,6 @@ class JSTester:
         new_pos = page.mainFrame().scrollPosition()
         assert old_pos != new_pos
 
-    def load(self, path, **kwargs):
-        """Load and display the given test data.
-
-        Args:
-            path: The path to the test file, relative to the javascript/
-                  folder.
-            **kwargs: Passed to jinja's template.render().
-        """
-        template = self._jinja_env.get_template(path)
-        with self._qtbot.waitSignal(self.webview.loadFinished) as blocker:
-            self.webview.setHtml(template.render(**kwargs))
-        assert blocker.args == [True]
-
     def run_file(self, filename):
         """Run a javascript file.
 
@@ -134,7 +218,57 @@ class JSTester:
         return self.webview.page().mainFrame().evaluateJavaScript(source)
 
 
+class JSWebEngineTester(JSTester):
+
+    """Object returned by js_tester_webengine which provides a webview.
+
+    Attributes:
+        webview: The webview which is used.
+        _qtbot: The QtBot fixture from pytest-qt.
+        _jinja_env: The jinja2 environment used to get templates.
+    """
+
+    def __init__(self, webview, qtbot):
+        super().__init__(webview, qtbot)
+        self.webview.setPage(TestWebEnginePage(self.webview))
+
+    def run_file(self, filename: str, expected) -> None:
+        """Run a javascript file.
+
+        Args:
+            filename: The javascript filename, relative to
+                      qutebrowser/javascript.
+            expected: The value expected return from the javascript execution
+        """
+        source = utils.read_file(os.path.join('javascript', filename))
+        self.run(source, expected)
+
+    def run(self, source: str, expected, world=None) -> None:
+        """Run the given javascript source.
+
+        Args:
+            source: The source to run as a string.
+            expected: The value expected return from the javascript execution
+            world: The scope the javascript will run in
+        """
+        if world is None:
+            world = QWebEngineScript.ApplicationWorld
+
+        callback_checker = helpers.utils.CallbackChecker(self._qtbot)
+        assert self.webview.settings().testAttribute(
+            QWebEngineSettings.JavascriptEnabled)
+        self.webview.page().runJavaScript(source, world,
+                                          callback_checker.callback)
+        callback_checker.check(expected)
+
+
 @pytest.fixture
-def js_tester(webview, qtbot):
-    """Fixture to test javascript snippets."""
-    return JSTester(webview, qtbot)
+def js_tester_webkit(webview, qtbot):
+    """Fixture to test javascript snippets in webkit."""
+    return JSWebKitTester(webview, qtbot)
+
+
+@pytest.fixture
+def js_tester_webengine(callback_checker, webengineview, qtbot):
+    """Fixture to test javascript snippets in webengine."""
+    return JSWebEngineTester(webengineview, qtbot)
diff --git a/tests/unit/javascript/position_caret/test_position_caret.py b/tests/unit/javascript/position_caret/test_position_caret.py
index 7be62e3cc..fcfa5cf5d 100644
--- a/tests/unit/javascript/position_caret/test_position_caret.py
+++ b/tests/unit/javascript/position_caret/test_position_caret.py
@@ -65,9 +65,9 @@ class CaretTester:
 
 
 @pytest.fixture
-def caret_tester(js_tester):
+def caret_tester(js_tester_webkit):
     """Helper fixture to test caret browsing positions."""
-    caret_tester = CaretTester(js_tester)
+    caret_tester = CaretTester(js_tester_webkit)
     # Showing webview here is necessary for test_scrolled_down_img to
     # succeed in some cases, see #1988
     caret_tester.js.webview.show()
diff --git a/tests/unit/javascript/stylesheet/green.css b/tests/unit/javascript/stylesheet/green.css
new file mode 100644
index 000000000..b2d035810
--- /dev/null
+++ b/tests/unit/javascript/stylesheet/green.css
@@ -0,0 +1 @@
+body, :root {background-color: rgb(0, 255, 0);}
diff --git a/tests/unit/javascript/stylesheet/none.css b/tests/unit/javascript/stylesheet/none.css
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/unit/javascript/stylesheet/simple.html b/tests/unit/javascript/stylesheet/simple.html
new file mode 100644
index 000000000..4073672a4
--- /dev/null
+++ b/tests/unit/javascript/stylesheet/simple.html
@@ -0,0 +1,4 @@
+{% extends "base.html" %}
+{% block content %}
+<p>Hello World!</p>
+{% endblock %}
diff --git a/tests/unit/javascript/stylesheet/simple.xml b/tests/unit/javascript/stylesheet/simple.xml
new file mode 100644
index 000000000..f9073de69
--- /dev/null
+++ b/tests/unit/javascript/stylesheet/simple.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Copyright 2017 suve <veg@svgames.pl> -->
+<component type="desktop">
+	<id>org.qutebrowser.qutebrowser</id>
+</component>
diff --git a/tests/unit/javascript/stylesheet/simple_bg_set_red.html b/tests/unit/javascript/stylesheet/simple_bg_set_red.html
new file mode 100644
index 000000000..b40352340
--- /dev/null
+++ b/tests/unit/javascript/stylesheet/simple_bg_set_red.html
@@ -0,0 +1,9 @@
+{% extends "base.html" %}
+{% block style %}
+body {
+    background-color: rgb(255, 0, 0);
+}
+{% endblock %}
+{% block content %}
+<p>Hello World!</p>
+{% endblock %}
diff --git a/tests/unit/javascript/stylesheet/test_appendchild.js b/tests/unit/javascript/stylesheet/test_appendchild.js
new file mode 100644
index 000000000..d1deadba6
--- /dev/null
+++ b/tests/unit/javascript/stylesheet/test_appendchild.js
@@ -0,0 +1,47 @@
+// Taken from acid3 bucket 5
+// https://github.com/w3c/web-platform-tests/blob/37cf5607a39357a0f213ab5df2e6b30499b0226f/acid/acid3/test.html#L2320
+
+// test 65: bring in a couple of SVG files and some HTML files dynamically - preparation for later tests in this bucket
+// NOTE FROM 2011 UPDATE: The svg.xml file still contains the SVG font, but it is no longer used
+kungFuDeathGrip = document.createElement('p');
+kungFuDeathGrip.className = 'removed';
+var iframe, object;
+// svg iframe
+iframe = document.createElement('iframe');
+iframe.onload = function () { kungFuDeathGrip.title += '1' };
+iframe.src = "svg.xml";
+kungFuDeathGrip.appendChild(iframe);
+// object iframe
+object = document.createElement('object');
+object.onload = function () { kungFuDeathGrip.title += '2' };
+object.data = "svg.xml";
+kungFuDeathGrip.appendChild(object);
+// xml iframe
+iframe = document.createElement('iframe');
+iframe.onload = function () { kungFuDeathGrip.title += '3' };
+iframe.src = "empty.xml";
+kungFuDeathGrip.appendChild(iframe);
+// html iframe
+iframe = document.createElement('iframe');
+iframe.onload = function () { kungFuDeathGrip.title += '4' };
+iframe.src = "empty.html";
+kungFuDeathGrip.appendChild(iframe);
+// html iframe
+iframe = document.createElement('iframe');
+iframe.onload = function () { kungFuDeathGrip.title += '5' };
+iframe.src = "xhtml.1";
+kungFuDeathGrip.appendChild(iframe);
+// html iframe
+iframe = document.createElement('iframe');
+iframe.onload = function () { kungFuDeathGrip.title += '6' };
+iframe.src = "xhtml.2";
+kungFuDeathGrip.appendChild(iframe);
+// html iframe
+iframe = document.createElement('iframe');
+iframe.onload = function () { kungFuDeathGrip.title += '7' };
+iframe.src = "xhtml.3";
+kungFuDeathGrip.appendChild(iframe);
+// add the lot to the document
+
+// Modified as we don't have a 'map'
+document.getElementsByTagName('head')[0].appendChild(kungFuDeathGrip);
diff --git a/tests/unit/javascript/stylesheet/test_stylesheet.py b/tests/unit/javascript/stylesheet/test_stylesheet.py
new file mode 100644
index 000000000..47a181d77
--- /dev/null
+++ b/tests/unit/javascript/stylesheet/test_stylesheet.py
@@ -0,0 +1,138 @@
+# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et:
+
+# Copyright 2017 Jay Kamat
+#
+# This file is part of qutebrowser.
+#
+# qutebrowser is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# qutebrowser is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with qutebrowser.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Tests for stylesheet.js."""
+
+import os
+import pytest
+
+QtWebEngineWidgets = pytest.importorskip("PyQt5.QtWebEngineWidgets")
+QWebEngineProfile = QtWebEngineWidgets.QWebEngineProfile
+
+from qutebrowser.utils import javascript
+
+try:
+    from qutebrowser.browser.webengine import webenginesettings
+except ImportError:
+    webenginesettings = None
+
+
+DEFAULT_BODY_BG = "rgba(0, 0, 0, 0)"
+GREEN_BODY_BG = "rgb(0, 255, 0)"
+CSS_BODY_GREEN = "body {background-color: rgb(0, 255, 0);}"
+CSS_BODY_RED = "body {background-color: rgb(255, 0, 0);}"
+
+
+class StylesheetTester:
+
+    """Helper class (for the stylesheet_tester fixture) for asserts.
+
+    Attributes:
+        js: The js_tester fixture.
+        config_stub: The config stub object.
+    """
+
+    def __init__(self, js_tester, config_stub):
+        self.js = js_tester
+        self.config_stub = config_stub
+
+    def init_stylesheet(self, css_file="green.css"):
+        """Initialize the stylesheet with a provided css file."""
+        css_path = os.path.join(os.path.dirname(__file__), css_file)
+        self.config_stub.val.content.user_stylesheets = css_path
+        p = QWebEngineProfile.defaultProfile()
+        webenginesettings._init_stylesheet(p)
+
+    def set_css(self, css):
+        """Set document style to `css` via stylesheet.js."""
+        code = javascript.assemble('stylesheet', 'set_css', css)
+        self.js.run(code, None)
+
+    def check_set(self, value, css_style="background-color",
+                  document_element="document.body"):
+        """Check whether the css in ELEMENT is set to VALUE."""
+        self.js.run("window.getComputedStyle({}, null)"
+                    ".getPropertyValue('{}');"
+                    .format(document_element,
+                            javascript.string_escape(css_style)), value)
+
+    def check_eq(self, one, two, true=True):
+        """Check if one and two are equal."""
+        self.js.run("{} === {};".format(one, two), true)
+
+
+@pytest.fixture
+def stylesheet_tester(js_tester_webengine, config_stub):
+    """Helper fixture to test stylesheets."""
+    ss_tester = StylesheetTester(js_tester_webengine, config_stub)
+    ss_tester.js.webview.show()
+    return ss_tester
+
+
+@pytest.mark.parametrize('page', ['stylesheet/simple.html',
+                                  'stylesheet/simple_bg_set_red.html'])
+def test_set_delayed(stylesheet_tester, page):
+    """Test a delayed invocation of set_css."""
+    stylesheet_tester.init_stylesheet("none.css")
+    stylesheet_tester.js.load(page)
+    stylesheet_tester.set_css("body {background-color: rgb(0, 255, 0);}")
+    stylesheet_tester.check_set("rgb(0, 255, 0)")
+
+
+@pytest.mark.parametrize('page', ['stylesheet/simple.html',
+                                  'stylesheet/simple_bg_set_red.html'])
+def test_set_clear_bg(stylesheet_tester, page):
+    """Test setting and clearing the stylesheet."""
+    stylesheet_tester.init_stylesheet()
+    stylesheet_tester.js.load('stylesheet/simple.html')
+    stylesheet_tester.check_set(GREEN_BODY_BG)
+    stylesheet_tester.set_css("")
+    stylesheet_tester.check_set(DEFAULT_BODY_BG)
+
+
+def test_set_xml(stylesheet_tester):
+    """Test stylesheet is applied without altering xml files."""
+    stylesheet_tester.init_stylesheet()
+    stylesheet_tester.js.load_file('stylesheet/simple.xml')
+    stylesheet_tester.check_set(GREEN_BODY_BG)
+    stylesheet_tester.check_eq('"html"', "document.documentElement.nodeName")
+
+
+def test_set_svg(stylesheet_tester):
+    """Test stylesheet is applied for svg files."""
+    stylesheet_tester.init_stylesheet()
+    stylesheet_tester.js.load_file('../../../misc/cheatsheet.svg')
+    stylesheet_tester.check_set(GREEN_BODY_BG,
+                                document_element="document.documentElement")
+    stylesheet_tester.check_eq('"svg"', "document.documentElement.nodeName")
+
+
+def test_set_error(stylesheet_tester):
+    """Test stylesheet modifies file not found error pages."""
+    stylesheet_tester.init_stylesheet()
+    stylesheet_tester.js.load_file('non-existent.html', force=True)
+    stylesheet_tester.check_set(GREEN_BODY_BG)
+
+
+def test_appendchild(stylesheet_tester):
+    stylesheet_tester.init_stylesheet()
+    stylesheet_tester.js.load('stylesheet/simple.html')
+    js_test_file_path = \
+        '../../tests/unit/javascript/stylesheet/test_appendchild.js'
+    stylesheet_tester.js.run_file(js_test_file_path, {})