Add unit tests for which.py (#1686)

* Add unit tests for which.py

* Change ls path to /bin/ls

* Update tests.sh

tests/unit-tests/test_which.py

@@ -0,0 +1,36 @@
+import sys
+from unittest.mock import MagicMock
+
+# Replace `pwndbg.commands` module with a mock to prevent import errors, as well
+# as the `load_commands` function
+module_name = "pwndbg.commands"
+module = MagicMock(__name__=module_name, load_commands=lambda: None)
+sys.modules[module_name] = module
+
+import os
+import tempfile
+
+# Load the mocks for the `gdb` and `gdblib` modules
+import mocks.gdb
+import mocks.gdblib  # noqa: F401
+
+# We must import the function under test after all the mocks are imported
+from pwndbg.lib.which import which
+
+
+def test_basic():
+    assert which("ls") == "/bin/ls"
+
+
+def test_nonexistent():
+    assert which("definitely-not-a-real-command") is None
+
+
+def test_dir():
+    with tempfile.TemporaryDirectory() as tempdir:
+        path = os.path.join(tempdir, "test_file")
+        with open(path, "w") as f:
+            f.write("test")
+        os.chmod(path, 0o755)
+
+        assert which(path) == path