function assertTableATableBJoin(relation, expectedIds) {
  assertEquals(expectedIds.length, relation.entries.length);
  relation.entries.forEach(function(entry, i) {
    assertEquals(2, Object.keys(entry.row.payload()).length);
    var expectedId = expectedIds[i];
    assertEquals(expectedId, entry.getField(ta['id']));
    assertEquals('dummyName' + expectedId, entry.getField(ta['name']));
    assertEquals(expectedId, entry.getField(tb['id']));
    assertEquals('dummyName' + expectedId, entry.getField(tb['name']));
  });
}
Asserts that the results of joining rows belonging to TableA and TableB is as
expected.
@param {!lf.proc.Relation} relation The joined relation.
@param {!Array<number>} expectedIds The IDs that are expected to appear in
    the results in the given order.