[Exp PyROOT] Add test for len in TCollection and subclasses

bindings/pyroot_experimental/PyROOT/test/CMakeLists.txt

@@ -16,3 +16,6 @@ ROOT_ADD_PYUNITTEST(pyroot_pyz_ttree_setbranchaddress ttree_setbranchaddress.py
                     COPY_TO_BUILDDIR TreeHelper.h)
 ROOT_ADD_PYUNITTEST(pyroot_pyz_ttree_branch ttree_branch.py
                     COPY_TO_BUILDDIR TreeHelper.h)
+
+# TCollection and subclasses pythonizations
+ROOT_ADD_PYUNITTEST(pyroot_pyz_tcollection_len tcollection_len.py)

bindings/pyroot_experimental/PyROOT/test/tcollection_len.py

+import unittest
+
+import ROOT
+
+
+class TCollectionLen(unittest.TestCase):
+    """
+    Test for the pythonization that allows to access the number of elements of a
+    TCollection (or subclass) by calling `len` on it.
+    """
+
+    num_elems = 3
+    tobject_list = [ ROOT.TObject() for _ in range(num_elems) ]
+
+    # Helpers
+    def add_elems_check_len(self, c):
+        for elem in self.tobject_list:
+            c.Add(elem)
+
+        self.assertEqual(len(c), self.num_elems)
+        self.assertEqual(len(c), c.GetEntries())
+
+    # Tests
+    def test_tlist(self):
+        self.add_elems_check_len(ROOT.TList())
+
+    def test_tobjarray(self):
+        self.add_elems_check_len(ROOT.TObjArray())
+
+    def test_thashtable(self):
+        self.add_elems_check_len(ROOT.THashTable())