                                     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)

                            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)

                                        let relation = relation._including(all: association)
                                        do {
                                            XCTAssertEqual(relation.children.count, 1)
                                            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: cardinality2.isSingular))
                                            XCTAssertEqual(relation.children[0].value.relation.children[0].value.kind, .bridge)
                                            XCTAssertEqual(relation.children[0].value.relation.children[0].value.relation.children.count, 1)
                                            XCTAssertEqual(relation.children[0].value.relation.children[0].value.relation.children[0].key, key3.name(singular: false))
                                            XCTAssertEqual(relation.children[0].value.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)
                                            XCTAssertEqual(relation.children[0].value.relation.children[0].key, key2.name(singular: cardinality2.isSingular))
                                            XCTAssertEqual(relation.children[0].value.relation.children[0].value.kind, .bridge)
                                            XCTAssertEqual(relation.children[0].value.relation.children[0].value.relation.children.count, 1)
