diff --git a/access.credentials b/access.credentials
new file mode 100644
index 0000000..7601807
--- /dev/null
+++ b/access.credentials
@@ -0,0 +1 @@
+baz
diff --git a/client.credentials b/client.credentials
new file mode 100644
index 0000000..3bd1f0e
--- /dev/null
+++ b/client.credentials
@@ -0,0 +1,2 @@
+foo
+bar
diff --git a/tests/test_constructor.py b/tests/test_constructor.py
new file mode 100644
index 0000000..720f58d
--- /dev/null
+++ b/tests/test_constructor.py
@@ -0,0 +1,21 @@
+import pytest
+from mastodon import Mastodon
+from mastodon.Mastodon import MastodonIllegalArgumentError
+
+def test_constructor_from_filenames():
+    api = Mastodon(
+            'client.credentials',
+            access_token = 'access.credentials')
+    assert api.client_id == 'foo'
+    assert api.client_secret == 'bar'
+    assert api.access_token == 'baz'
+
+def test_constructor_illegal_ratelimit():
+    with pytest.raises(MastodonIllegalArgumentError):
+        api = Mastodon(
+                'foo', client_secret='bar',
+                ratelimit_method='baz')
+
+def test_constructor_missing_client_secret():
+    with pytest.raises(MastodonIllegalArgumentError):
+        api = Mastodon('foo')