config: read merged config by default (#5179)

* config: read merged config by default

* tests: move root test out of config tests

* tests: refactor config tests

* cli: fix cache dir command

tests/func/test_root.py

@@ -0,0 +1,13 @@
+from dvc.main import main
+
+
+def test_root(tmp_dir, dvc, caplog):
+    assert main(["root"]) == 0
+    assert ".\n" in caplog.text
+
+
+def test_root_locked(tmp_dir, dvc, caplog):
+    # NOTE: check that `dvc root` is not blocked with dvc lock
+    with dvc.lock:
+        assert main(["root"]) == 0
+    assert ".\n" in caplog.text