Add test_shelloracle.py

tests/test_shelloracle.py

@@ -0,0 +1,26 @@
+import os
+import sys
+
+import pytest
+
+from shelloracle.shelloracle import get_query_from_pipe
+
+
+def test_get_query_from_pipe(monkeypatch):
+    # Is a TTY
+    monkeypatch.setattr(os, "isatty", lambda _: True)
+    assert get_query_from_pipe() is None
+
+    # Not a TTY and no lines in the pipe
+    monkeypatch.setattr(os, "isatty", lambda _: False)
+    monkeypatch.setattr(sys.stdin, "readlines", lambda: [])
+    assert get_query_from_pipe() is None
+
+    # Not TTY and one line in the pipe
+    monkeypatch.setattr(sys.stdin, "readlines", lambda: ["what is up"])
+    assert get_query_from_pipe() == "what is up"
+
+    # Not a TTY and multiple lines in the pipe
+    monkeypatch.setattr(sys.stdin, "readlines", lambda: ["what is up", "what is down"])
+    with pytest.raises(ValueError):
+        get_query_from_pipe()