diff --git a/.ci/atime/tests.R b/.ci/atime/tests.R
index f6d68ce68..511079477 100644
--- a/.ci/atime/tests.R
+++ b/.ci/atime/tests.R
@@ -231,7 +231,20 @@ test.list <- atime::atime_test_list(
     },
     expr = data.table:::melt(DT, measure.vars = measure.vars),
     Slow = "fd24a3105953f7785ea7414678ed8e04524e6955", # Parent of the merge commit (https://github.com/Rdatatable/data.table/commit/ed72e398df76a0fcfd134a4ad92356690e4210ea) of the PR (https://github.com/Rdatatable/data.table/pull/5054) that fixes the issue
-    Fast = "ed72e398df76a0fcfd134a4ad92356690e4210ea"), # Merge commit of the PR (https://github.com/Rdatatable/data.table/pull/5054) that fixes the issue
+    Fast = "ed72e398df76a0fcfd134a4ad92356690e4210ea"), # Merge commit of the PR (https://github.com/Rdatatable/data.table/pull/5054) that fixes the issue  # Test case created directly using the atime code below (not adapted from any other benchmark), based on the issue/fix PR https://github.com/Rdatatable/data.table/pull/5054#issue-930603663 "melt should be more efficient when there are missing input columns."
+
+  # Test case created from @tdhock's comment https://github.com/Rdatatable/data.table/pull/6393#issuecomment-2327396833, in turn adapted from @philippechataignon's comment https://github.com/Rdatatable/data.table/pull/6393#issuecomment-2326714012
+  "fwrite refactored in #6393" = atime::atime_test(
+    setup = {
+      set.seed(1)
+      NC = 10L
+      L <- data.table(i=1:N)
+      L[, paste0("V", 1:NC) := replicate(NC, rnorm(N), simplify=FALSE)]
+      out.csv <- tempfile()
+    },
+    expr = data.table::fwrite(L, out.csv, compress="gzip"),
+    Before = "f339aa64c426a9cd7cf2fcb13d91fc4ed353cd31", # Parent of the first commit https://github.com/Rdatatable/data.table/commit/fcc10d73a20837d0f1ad3278ee9168473afa5ff1 in the PR https://github.com/Rdatatable/data.table/pull/6393/commits with major change to fwrite with gzip.
+    PR = "3630413ae493a5a61b06c50e80d166924d2ef89a"), # Close-to-last merge commit in the PR.
 
   tests=extra.test.list)
 # nolint end: undesirable_operator_linter.