diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..068f0e8
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,21 @@
+from fediverse_blocklist_tool.cli import get_format_from_filename
+
+
+def test_get_format_from_filename():
+    assert "toml" == get_format_from_filename("temp.toml")
+    assert "csv" == get_format_from_filename("temp.csv")
+    assert "json" == get_format_from_filename("temp.json")
+    assert "md" == get_format_from_filename("temp.md")
+
+    assert "md" == get_format_from_filename("csv.md")
+    assert "md" == get_format_from_filename("toml.md")
+    assert "md" == get_format_from_filename("json.md")
+
+    assert "toml" == get_format_from_filename("csv.toml")
+    assert "toml" == get_format_from_filename("md.toml")
+    assert "toml" == get_format_from_filename("json.toml")
+    assert "toml" == get_format_from_filename("tmp")
+
+    assert "json" == get_format_from_filename("csv.json")
+    assert "json" == get_format_from_filename("md.json")
+    assert "json" == get_format_from_filename("toml.json")