From 151af13be2307525f1bf765e59f5817942063b48 Mon Sep 17 00:00:00 2001
From: Ryan Krattiger <80296582+kwryankrattiger@users.noreply.github.com>
Date: Mon, 24 Mar 2025 11:25:45 -0500
Subject: [PATCH] Unit tests: error message when running parallel without xdist
 (#49632)

---
 lib/spack/spack/cmd/unit_test.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/spack/spack/cmd/unit_test.py b/lib/spack/spack/cmd/unit_test.py
index eadd45ba824..dcd7caf6b9c 100644
--- a/lib/spack/spack/cmd/unit_test.py
+++ b/lib/spack/spack/cmd/unit_test.py
@@ -17,6 +17,7 @@
     pytest = None  # type: ignore
 
 import llnl.util.filesystem
+import llnl.util.tty as tty
 import llnl.util.tty.color as color
 from llnl.util.tty.colify import colify
 
@@ -236,6 +237,12 @@ def unit_test(parser, args, unknown_args):
         pytest_root = spack.extensions.load_extension(args.extension)
 
     if args.numprocesses is not None and args.numprocesses > 1:
+        try:
+            import xdist  # noqa: F401
+        except ImportError:
+            tty.error("parallel unit-test requires pytest-xdist module")
+            return 1
+
         pytest_args.extend(
             [
                 "--dist",