[PyROOT exp] Add test for string_view backport

bindings/pyroot_experimental/PyROOT/test/CMakeLists.txt

@@ -81,3 +81,6 @@ if(roofit)
   # RooDataHist pythonisations
   ROOT_ADD_PYUNITTEST(pyroot_pyz_roodatahist_ploton roodatahist_ploton.py)
 endif()
+
+# std::string_view backport in CPyCppyy
+ROOT_ADD_PYUNITTEST(pyroot_string_view_backport string_view_backport.py)

bindings/pyroot_experimental/PyROOT/test/string_view_backport.py

+import unittest
+import ROOT
+
+
+class StringViewBackport(unittest.TestCase):
+    """
+    Test the availability of std::string_view since ROOT has a backport to C++11
+    """
+
+    def test_interpreter(self):
+        ROOT.gInterpreter.Declare("std::string TestStringViewBackport(std::string_view x) { return std::string(x); }")
+        x = ROOT.TestStringViewBackport("foo")
+        self.assertEqual(str(x), "foo")
+
+    def test_rdataframe(self):
+        df = ROOT.ROOT.RDataFrame("tree", "file.root")
+        self.assertEqual(str(df), "A data frame built on top of the tree dataset.")
+
+
+if __name__ == '__main__':
+    unittest.main()