add some test cases re flatgraph compat mode (ShiftLeftSecurity#427)

* add some test cases re flatgraph compat mode

* add comment to clarify/warn the reader

Author: mpollmeier

core-tests/src/test/java/overflowdb/ElementTest.java

@@ -38,7 +38,6 @@ public void overviewTest() {
               TestNode.LABEL,
               TestNode.STRING_PROPERTY, "node 2",
               TestNode.INT_PROPERTY, 52,
-              TestNode.STRING_LIST_PROPERTY, Arrays.asList("stringThree", "stringFour"),
               TestNode.INT_LIST_PROPERTY, Arrays.asList(52, 53));
 
       builder.addEdge(n1D, n2D,TestEdge.LABEL, TestEdge.LONG_PROPERTY, 99L);
@@ -49,13 +48,23 @@ public void overviewTest() {
       Node n2 = (Node)n2D.getRefOrId();
       Edge e = n1.outE().next();
 
-      //  verify that we can cast to our domain-specific nodes/edges
+      // verify that we can cast to our domain-specific nodes/edges
+      // n.b. the results of `property` and `propertyOption` accessors depend on the domain class implementations
+      // and might therefor be misleading - see e.g. https://github.com/joernio/joern/pull/4382: our codegen generates domain
+      // classes that return `Some(Seq.empty)` for an undefined list property...
       TestNode node1 = (TestNode) n1;
+      TestNode node2 = (TestNode) n2;
       assertEquals("node 1", node1.stringProperty());
       assertEquals("node 1", node1.property(TestNode.STRING_PROPERTY));
       assertEquals("node 1", node1.property(new PropertyKey<>(TestNode.STRING_PROPERTY)));
       assertEquals(Optional.of("node 1"), node1.propertyOption(TestNode.STRING_PROPERTY));
       assertEquals(Optional.of("node 1"), node1.propertyOption(new PropertyKey<>(TestNode.STRING_PROPERTY)));
+      assertEquals(Optional.of(Arrays.asList("stringOne", "stringTwo")), node1.propertyOption(TestNode.STRING_LIST_PROPERTY));
+      assertEquals(Optional.of(Arrays.asList("stringOne", "stringTwo")), node1.propertyOption(new PropertyKey<>(TestNode.STRING_LIST_PROPERTY)));
+      assertEquals(Optional.empty(), node1.propertyOption("UNKNOWN_PROPERTY"));
+      assertEquals(Optional.empty(), node1.propertyOption(new PropertyKey<>("UNKNOWN_PROPERTY")));
+      assertEquals(Optional.empty(), node2.propertyOption(TestNode.STRING_LIST_PROPERTY));
+      assertEquals(Optional.empty(), node2.propertyOption(new PropertyKey<>(TestNode.STRING_LIST_PROPERTY)));
       assertEquals(Integer.valueOf(42), node1.intProperty());
       assertEquals(Arrays.asList("stringOne", "stringTwo"), node1.stringListProperty());
       assertEquals(Arrays.asList(42, 43), node1.intListProperty());