x <- sql.join(Album, Artist, "inner", on = x.ArtistId == 2*y.ArtistId)
x <- sql.join(Album, Artist, "left", on = x.ArtistId == 2*y.ArtistId)
x <- sql.join(Album, Artist, "right", on = x.ArtistId == 2*y.ArtistId)
x <- sql.join(Album, Artist, "outer", on = x.ArtistId == 2*y.ArtistId)
test_that("cross join throws warning when on != NULL", {
x <- sql.join(Album, Artist, "cross", on = x.ArtistId == 2*y.ArtistId)
x <- sql.join(Album, Album, on = x.ArtistId == y.AlbumId)

"cross join throws warning when on != NULL"