expect_equal <- function(x, y) {
  stopifnot(isTRUE(all.equal(x, y)))
}

library(reclin2)

x <- data.table(a = c(1,1,2,2), b = c(1,2,1,2))
y <- data.table(a = c(3,3,2,2), b = c(1,2,1,2))

pairs <- pair_blocking(x, y, on = "a")
expect_equal(names(pairs), c(".x", ".y"))
expect_equal(pairs$.x, c(3,3,4,4))
expect_equal(pairs$.y, c(3,4,3,4))
expect_equal(attr(pairs, "x"), x)
expect_equal(attr(pairs, "y"), y)

pairs <- pair_blocking(x, y, on = "a", add_xy = FALSE)
expect_equal(attr(pairs, "x"), NULL)
expect_equal(attr(pairs, "y"), NULL)

pairs <- pair_blocking(x, on = "a", deduplication = TRUE)
expect_equal(names(pairs), c(".x", ".y"))
expect_equal(pairs$.x, c(1,3))
expect_equal(pairs$.y, c(2,4))