add test for situation found in https://github.com/dgtlmoon/changedetection.io/pull/749#issuecomment-1200154861

changedetectionio/tests/test_diff_filter_changes_as_add_delete.py

@@ -0,0 +1,72 @@
+#!/usr/bin/python3
+
+import time
+from flask import url_for
+from .util import live_server_setup
+
+def set_original_response():
+    test_return_data = """
+        Here
+        is
+        some
+        text
+    """
+
+    with open("test-datastore/endpoint-content.txt", "w") as f:
+        f.write(test_return_data)
+
+def set_all_new_response():
+    test_return_data = """
+        brand
+        new
+        words
+    """
+
+    with open("test-datastore/endpoint-content.txt", "w") as f:
+        f.write(test_return_data)
+
+def test_diff_filter_changes_as_add_delete(client, live_server):
+    live_server_setup(live_server)
+
+    sleep_time_for_fetch_thread = 3
+
+    set_original_response()
+    # Give the endpoint time to spin up
+    time.sleep(1)
+
+    # Add our URL to the import page
+    test_url = url_for('test_endpoint', _external=True)
+    res = client.post(
+        url_for("import_page"),
+        data={"urls": test_url},
+        follow_redirects=True
+    )
+
+    assert b"1 Imported" in res.data
+    time.sleep(sleep_time_for_fetch_thread)
+
+    # Add our URL to the import page
+    res = client.post(
+        url_for("edit_page", uuid="first"),
+        data={"trigger_add": "y",
+              "trigger_del": "n",
+              "url": test_url,
+              "fetch_backend": "html_requests"},
+        follow_redirects=True
+    )
+    assert b"Updated watch." in res.data
+    assert b'unviewed' not in res.data
+
+    #  Make an delete change
+    set_all_new_response()
+
+    time.sleep(sleep_time_for_fetch_thread)
+    # Trigger a check
+    client.get(url_for("form_watch_checknow"), follow_redirects=True)
+
+    # Give the thread time to pick it up
+    time.sleep(sleep_time_for_fetch_thread)
+
+    # We should see the change
+    res = client.get(url_for("index"))
+    assert b'unviewed' in res.data