diff --git a/src/calibre/utils/rapydscript.py b/src/calibre/utils/rapydscript.py
index 05bd9e3782..e90fb20673 100644
--- a/src/calibre/utils/rapydscript.py
+++ b/src/calibre/utils/rapydscript.py
@@ -329,6 +329,59 @@ def atomic_write(base, name, content):
     atomic_rename(tname, name)
 
 
+def run_rapydscript_tests():
+    from PyQt5.QtWebEngineWidgets import QWebEnginePage, QWebEngineScript
+    from PyQt5.Qt import QApplication, QEventLoop
+    from calibre.gui2.webengine import secure_webengine
+    from calibre.gui2 import must_use_qt
+    must_use_qt()
+    base = base_dir()
+    rapydscript_dir = os.path.join(base, 'src', 'pyj')
+    fname = os.path.join(rapydscript_dir, 'test.pyj')
+    with lopen(fname, 'rb') as f:
+        js = compile_fast(f.read(), fname)
+
+    def create_script(src, name):
+        s = QWebEngineScript()
+        s.setName(name)
+        s.setInjectionPoint(QWebEngineScript.DocumentReady)
+        s.setWorldId(QWebEngineScript.ApplicationWorld)
+        s.setRunsOnSubFrames(False)
+        s.setSourceCode(src)
+        return s
+
+    class Tester(QWebEnginePage):
+
+        def __init__(self):
+            QWebEnginePage.__init__(self)
+            self.titleChanged.connect(self.title_changed)
+            secure_webengine(self)
+            self.scripts().insert(create_script(js, 'test-rapydscript.js'))
+            self.setHtml('<p>initialize')
+            self.working = True
+
+        def title_changed(self, title):
+            if title == 'initialized':
+                self.titleChanged.disconnect()
+                self.runJavaScript('window.main()', QWebEngineScript.ApplicationWorld, self.callback)
+
+        def spin_loop(self):
+            while self.working:
+                QApplication.instance().processEvents(QEventLoop.ExcludeUserInputEvents)
+            return self.result
+
+        def callback(self, result):
+            self.result = result
+            self.working = False
+
+        def javaScriptConsoleMessage(self, level, msg, line_num, source_id):
+            print(msg, file=sys.stderr if level > 0 else sys.stdout)
+
+    tester = Tester()
+    result = tester.spin_loop()
+    raise SystemExit(int(result))
+
+
 def compile_editor():
     base = base_dir()
     rapydscript_dir = os.path.join(base, 'src', 'pyj')
diff --git a/src/pyj/test.pyj b/src/pyj/test.pyj
new file mode 100644
index 0000000000..aea7d9f841
--- /dev/null
+++ b/src/pyj/test.pyj
@@ -0,0 +1,47 @@
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2020, Kovid Goyal <kovid at kovidgoyal.net>
+from __python__ import bound_methods, hash_literals
+
+import traceback
+
+from testing import registered_tests, reset_dom
+
+
+def get_matching_tests_for_name(name):
+    ans = []
+    for k in Object.keys(registered_tests):
+        q = k.split('.')[-1]
+        if not name or q is name:
+            ans.append(registered_tests[k])
+    return ans
+
+
+def run_tests(tests):
+    failed_tests = []
+    count = 0
+    for f in tests:
+        print(f.test_name, '...')
+        reset_dom()
+        try:
+            f()
+            count += 1
+        except:
+            traceback.print_stack()
+            failed_tests.append((f.test_name, traceback.format_stack()))
+    return failed_tests, count
+
+
+def main():
+    tests = get_matching_tests_for_name()
+    st = window.performance.now()
+    failed_tests, total = run_tests(tests)
+    time = window.performance.now() - st
+    if failed_tests.length:
+        console.error(f'{failed_tests.length} out of {total} failed in {time:.1f} seconds')
+    else:
+        print(f'Ran {total} tests in {time:.1f} seconds')
+    return 1 if failed_tests.length else 0
+
+
+window.main = main
+document.title = 'initialized'
diff --git a/src/pyj/testing.pyj b/src/pyj/testing.pyj
new file mode 100644
index 0000000000..ffdc037158
--- /dev/null
+++ b/src/pyj/testing.pyj
@@ -0,0 +1,78 @@
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2020, Kovid Goyal <kovid at kovidgoyal.net>
+from __python__ import bound_methods, hash_literals
+
+from dom import clear
+
+def raise_fail(preamble, msg):
+    if msg:
+        msg = '. ' + msg
+    else:
+        msg = ''
+    raise AssertionError(preamble + msg)
+
+
+def assert_equal(a, b, msg):
+
+    def fail():
+        raise_fail(f'{a} != {b}', msg)
+
+    atype = jstype(a)
+    btype = jstype(b)
+    base_types = {'number': True, 'boolean': True, 'string': True, 'undefined': True}
+    if base_types[a] or base_types[b] or a is None or b is None:
+        if a is not b:
+            fail()
+        return
+    if a.__eq__:
+        if not a.__eq__(b):
+            fail()
+        return
+    if b.__eq__:
+        if not b.__eq__(a):
+            fail()
+        return
+    if a.length? or b.length?:
+        if a.length is not b.length:
+            fail()
+        for i in range(a.length):
+            assert_equal(a[i], b[i])
+        return
+    if atype is 'object':
+        for key in Object.keys(a):
+            assert_equal(a[key], b[key])
+    if btype is 'object':
+        for key in Object.keys(b):
+            assert_equal(a[key], b[key])
+
+    if a is not b:
+        fail()
+
+
+def assert_true(x, msg):
+    if not x:
+        raise_fail(f'{x} is not truthy', msg)
+
+
+def assert_fale(x, msg):
+    if x:
+        raise_fail(f'{x} is truthy', msg)
+
+
+def reset_dom():
+    html = document.documentElement
+    clear(html)
+    head = document.createElement('head')
+    body = document.createElement('body')
+    html.appendChild(head)
+    html.appendChild(body)
+
+
+registered_tests = {}
+
+
+def test(f):
+    mod = f.__module__ or 'unknown_test_module'
+    f.test_name = mod + '.' + f.name
+    registered_tests[f.test_name] = f
+    return f