tests: add some data tests

tests/test_gt_data.py

@@ -0,0 +1,27 @@
+import pandas as pd
+
+from gt._gt_data import Stub, RowInfo
+from gt._gt_data import RowGroups
+
+
+def test_stub_construct_manual():
+    stub = Stub([RowInfo(0), RowInfo(1)])
+    assert stub[0] == RowInfo(0)
+
+
+def test_stub_construct_df():
+    stub = Stub(pd.DataFrame({"x": [8, 9]}))
+
+    assert len(stub) == 2
+    assert stub[0] == RowInfo(0)
+    assert stub[1] == RowInfo(1)
+
+
+def test_row_groups_construct_manual():
+    groups = RowGroups(["a", "b"])
+
+    assert len(groups) == 2
+    assert groups[0] == "a"
+    assert groups[1] == "b"
+
+    assert isinstance(groups[:], RowGroups)