diff --git a/tests/unit/browser/webengine/test_webenginetab.py b/tests/unit/browser/webengine/test_webenginetab.py
new file mode 100644
index 000000000..d6ecc2b5e
--- /dev/null
+++ b/tests/unit/browser/webengine/test_webenginetab.py
@@ -0,0 +1,107 @@
+# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et:
+
+# Copyright 2018 Florian Bruhin (The Compiler) <mail@qutebrowser.org>
+#
+# 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/>.
+
+"""Test webenginetab."""
+
+from unittest import mock
+import logging
+
+from PyQt5.QtCore import QObject
+from PyQt5.QtWebEngineWidgets import QWebEnginePage, QWebEngineScriptCollection
+import pytest
+
+from qutebrowser.browser.webengine.webenginetab import _WebEngineScripts
+from qutebrowser.browser.greasemonkey import GreasemonkeyScript
+
+pytestmark = pytest.mark.usefixtures('greasemonkey_manager')
+
+
+class TestWebengineScripts:
+    """Test the _WebEngineScripts utility class."""
+
+    class FakeWidget(QObject):
+        """Fake widget for _WebengineScripts to use."""
+
+        def __init__(self, *args, **kwargs):
+            super().__init__(*args, **kwargs)
+            self.scripts = []
+            self.page = mock.create_autospec(QWebEnginePage)
+            self.scripts_mock = mock.create_autospec(
+                QWebEngineScriptCollection
+            )
+            self.scripts_mock.toList.return_value = self.scripts
+            self.page.return_value.scripts.return_value = self.scripts_mock
+
+    def test_greasemonkey_undefined_world(self, fake_web_tab, caplog):
+        """Make sure scripts with non-existent worlds are rejected."""
+        uut = _WebEngineScripts(fake_web_tab)
+        uut._widget = self.FakeWidget()
+        scripts = [
+            GreasemonkeyScript([('qute-js-world', 'Mars')], None)
+        ]
+
+        with caplog.at_level(logging.ERROR, 'greasemonkey'):
+            uut._inject_greasemonkey_scripts(scripts)
+
+        assert len(caplog.records) == 1
+        msg = caplog.records[0].message
+        assert "has invalid value for '@qute-js-world': Mars" in msg
+        uut._widget.scripts_mock.insert.assert_not_called()
+
+    @pytest.mark.parametrize("worldid", [
+        -1, 257
+    ])
+    def test_greasemonkey_out_of_range_world(self, worldid,
+                                             fake_web_tab, caplog):
+        """Make sure scripts with out-of-range worlds are rejected."""
+        uut = _WebEngineScripts(fake_web_tab)
+        uut._widget = self.FakeWidget()
+        scripts = [
+            GreasemonkeyScript([('qute-js-world', worldid)], None)
+        ]
+
+        with caplog.at_level(logging.ERROR, 'greasemonkey'):
+            uut._inject_greasemonkey_scripts(scripts)
+
+        assert len(caplog.records) == 1
+        msg = caplog.records[0].message
+        assert "has invalid value for '@qute-js-world': " in msg
+        assert "should be between 0 and" in msg
+        uut._widget.scripts_mock.insert.assert_not_called()
+
+    @pytest.mark.parametrize("worldid", [
+        0, 10
+    ])
+    def test_greasemonkey_good_worlds_are_passed(self, worldid,
+                                                 fake_web_tab, caplog):
+        """Make sure scripts with valid worlds have it set."""
+        uut = _WebEngineScripts(fake_web_tab)
+        uut._widget = self.FakeWidget()
+        scripts = [
+            GreasemonkeyScript(
+                [('name', 'foo'), ('qute-js-world', worldid)], None
+            )
+        ]
+
+        with caplog.at_level(logging.ERROR, 'greasemonkey'):
+            uut._inject_greasemonkey_scripts(scripts)
+
+        calls = uut._widget.scripts_mock.insert.call_args_list
+        assert len(calls) == 1
+        assert calls[0][0][0].worldId() == worldid