add tests for the headers functions

tests/test_header.py

@@ -0,0 +1,12 @@
+import url2markdown.header as header
+
+
+def test_build_header_dict(create_article):
+    article = create_article()
+    header._build_header_dict(article)
+    assert False
+
+
+def test_get_topics_from_cli():
+    header._get_topics_from_cli()
+    assert False