add pytest

tests/test_html.py

@@ -0,0 +1,17 @@
+from nicegui import html, ui
+from nicegui.testing import Screen
+
+
+def test_html_element(screen: Screen):
+    ui.html('This is strong.', tag='strong')
+
+    screen.open('/')
+    assert screen.find_by_tag('strong').text == 'This is strong.'
+
+
+def test_html_button(screen: Screen):
+    html.button('Click me').on('click', lambda: ui.notify('Hi!'))
+
+    screen.open('/')
+    screen.click('Click me')
+    screen.should_contain('Hi!')