                             let relation = relation._including(all: association)
                             do {
                                 XCTAssertEqual(relation.children.count, 1)
-                                // TODO: what is the purpose of the name of the `.bridge` children, from the point of view of the user?
-                                //                                                           ~~~~~~~~~~~~~~~~~~~~~~~
                                 XCTAssertEqual(relation.children[0].key, key1.name(singular: cardinality1.isSingular))
                                 XCTAssertEqual(relation.children[0].value.kind, .bridge)
                                 XCTAssertEqual(relation.children[0].value.relation.children.count, 1)

                                    XCTAssertEqual(relation.children[0].value.relation.children[0].key, key2.name(singular: true))
                                    XCTAssertEqual(relation.children[0].value.relation.children[0].value.kind, .oneRequired)
                                }
                                // TODO: what is the purpose of the name of the `.bridge` children, from the point of view of the user?
                                // ~~~~~~~~~~~~~~~~~~~~~~~~
                                if !cardinality1.isSingular && key1.name(singular: true) != key1.name(singular: false) {
                                    let relation = relation._including(all: association)
                                    XCTAssertEqual(relation.children.count, 2)

                                XCTAssertEqual(relation.children[0].value.relation.children[0].value.kind, .all)
                            }
                            
                            // TODO: here we see the problem: it should be possible to merge association1 when it is singular.
                            if !cardinality1.isSingular && key1.name(singular: true) != key1.name(singular: false) {
                                let relation = relation._joining(optional: association1)
                                XCTAssertEqual(relation.children.count, 2)
                                XCTAssertEqual(relation.children[0].key, key1.name(singular: cardinality1.isSingular))
                                XCTAssertEqual(relation.children[0].value.kind, .bridge)
                                XCTAssertEqual(relation.children[0].value.relation.children.count, 1)
