Merge test_pandas.py into test_madx.py again

.github/workflows/build.yml

@@ -216,12 +216,12 @@ jobs:
       - run: flake8
 
       - run: coverage run --source=cpymad -p -m pytest test/test_util.py -v
-      - run: coverage run --source=cpymad -p -m pytest test/test_madx.py -v
+      - run: coverage run --source=cpymad -p -m pytest test/test_madx.py -v -k "not dframe"
       - run: coverage run --source=cpymad -p -m pytest test/test_regression.py -v
       - run: coverage run --source=cpymad -p -m pytest test/test_transfer_map.py -v
 
       - run: pip install pandas
-      - run: coverage run --source=cpymad -p -m pytest test/test_pandas.py -v
+      - run: coverage run --source=cpymad -p -m pytest test/test_madx.py -v -k "dframe"
 
       - run: coverage combine
       - run: coveralls

test/test_madx.py

@@ -843,6 +843,45 @@ def test_errors(mad):
     assert_allclose(al.dy, -4e-3)
 
 
+def test_dframe_after_use(mad):
+    mad.input("""
+        mqf.k1 =  0.3037241107;
+        mqd.k1 = -0.3037241107;
+
+        fodo: sequence, l=10, refer=entry;
+        mqf: quadrupole, at=0, l=1, k1:=mqf.k1;
+        dff: drift,      at=1, l=4;
+        mqd: quadrupole, at=5, l=1, k1:=mqd.k1;
+        dfd: drift,      at=6, l=4;
+        endsequence;
+
+        beam;
+        use, sequence=fodo;
+        twiss, sequence=fodo, x=0.1;
+    """)
+    index = ['#s', 'mqf', 'dff', 'mqd', 'dfd', '#e']
+    names = ['fodo$start', 'mqf', 'dff', 'mqd', 'dfd', 'fodo$end']
+
+    twiss = mad.table.twiss
+    assert index == twiss.row_names()
+    assert index == twiss.dframe().index.tolist()
+    assert names == twiss.dframe(index='name').index.tolist()
+
+    mad.use(sequence='fodo')
+
+    twiss = mad.table.twiss
+
+    # Should still work:
+    assert names == twiss.dframe(index='name').index.tolist()
+
+    # The following assert demonstrates the current behaviour and is
+    # meant to detect if the MAD-X implementation changes. It may lead
+    # to crashes or change in the future. In that case, please remove
+    # this line. It does not represent desired behaviour!
+    assert mad.table.twiss.row_names() == \
+        ['#s', '#e', 'dfd', 'mqd', 'dff', 'mqf']
+
+
 def _get_elems(mad, seq_name):
     elems = mad.sequence[seq_name].elements
     elem_idx = dict((el.node_name, i) for i, el in enumerate(elems))