Test operator result.elemental_mass on an RST (#1541)

* Test operator result.elemental_mass on an RST

Signed-off-by: paul.profizi <paul.profizi@ansys.com>

* Fix retro-compatibility

Signed-off-by: paul.profizi <paul.profizi@ansys.com>

* Fix retro-compatibility

Signed-off-by: paul.profizi <paul.profizi@ansys.com>

---------

Signed-off-by: paul.profizi <paul.profizi@ansys.com>

tests/operators/test_operator_elemental_mass.py

@@ -0,0 +1,19 @@
+import conftest
+import pytest
+import ansys.dpf.core as dpf
+
+
+@pytest.mark.skipif(
+    not conftest.SERVERS_VERSION_GREATER_THAN_OR_EQUAL_TO_8_2,
+    reason="Elemental mass operator not functional before 8.2,",
+)
+def test_operator_elemental_mass_rst(allkindofcomplexity):
+    model = dpf.Model(allkindofcomplexity)
+    op = dpf.operators.result.elemental_mass(data_sources=model)
+    fc = op.eval()
+    assert len(fc) == 1
+    field: dpf.Field = fc[0]
+    assert field.scoping.size == 9271
+    assert field.component_count == 1
+    assert field.location == dpf.locations.elemental
+    assert field.unit == "kg"