add test_etherpad

tests/test_etherpad.py

+from configparser import ConfigParser
+from functools import cache
+from protocol_translator.pad import Etherpad
+
+
+@cache
+def init():
+    api_keys = ConfigParser()
+
+    api_keys.read("api_keys.conf")
+
+    e = Etherpad("https://collab.fem-net.de/pad/p/test2",
+                 api_keys["default"]["etherpad_key"])
+
+    return e
+
+
+def test_init():
+    e = init()
+    assert isinstance(e, pad.Etherpad)
+
+
+def test_read():
+    e = init()
+    assert e.read() == "testtest"
+
+
+def test_write():
+    e = init()