extract DT setup from test

Author: czeildi

inst/tests/tests.Rraw

@@ -21841,8 +21841,9 @@ test(2343.2, forderv(list(x)), integer(0))
 # Keep key when new column added before existing key in j
 # Incorrect key can lead to incorrect join result #7364
 local({
-  test(2344.00, key(data.table(V1 = 1:2, key = "V1")[, .(V2 = c("b", "a"), V1)]), "V1")
-  test(2344.01, key(data.table(V1 = 1:2, key = "V1")[, .(V2 = -V1, V1)]), "V1")
+  DT = data.table(V1 = 1:2, key = "V1")
+  test(2344.00, key(DT[, .(V2 = c("b", "a"), V1)]), "V1")
+  test(2344.01, key(DT[, .(V2 = -V1, V1)]), "V1")
 
   d1 = data.table(
     V1 = c(1L, 0L, 1L),