Add test for cube() support with .SDcols patterns (issue #7354)

Author: nityasingh07

tests/tests-cube-sdcols.R

@@ -0,0 +1,21 @@
+# tests/tests-cube-sdcols.R
+# Test: cube() support for patterns with .SDcols
+# Related issue: https://github.com/Rdatatable/data.table/issues/7354
+
+library(data.table)
+
+cat("Running test for cube() with .SDcols pattern...\n")
+
+DT <- data.table(a1 = 1:2, a2 = 3:4, b = 5:6)
+
+result <- tryCatch({
+  cube(DT, .SDcols = patterns("^a"))
+  "No error"
+}, error = function(e) {
+  paste("Error:", e$message)
+})
+
+cat("Result:", result, "\n")
+
+# Expected: Should ideally handle .SDcols with patterns, but currently errors.
+