zfs: expand testing to include a failing multi case

tests/zfs.nix

@@ -25,6 +25,11 @@ testPkgs.testers.runNixOSTest {
         # Test multi-command logic: service with multiple serviceMountWithZpool calls
         (lib.serviceMountWithZpool "multi-service" "rpool" [ "/mnt/rpool_data" ])
         (lib.serviceMountWithZpool "multi-service" "rpool2" [ "/mnt/rpool2_data" ])
+
+        # Test multi-command logic: service with multiple serviceMountWithZpool calls
+        # BUT this one should fail as `/mnt/rpool_moar_data` is not on rpool2
+        (lib.serviceMountWithZpool "multi-service-fail" "rpool" [ "/mnt/rpool_data" ])
+        (lib.serviceMountWithZpool "multi-service-fail" "rpool2" [ "/mnt/rpool_moar_data" ])
       ];
 
       virtualisation = {
@@ -68,6 +73,14 @@ testPkgs.testers.runNixOSTest {
           ExecStart = lib.getExe pkgs.bash;
         };
       };
+
+      systemd.services."multi-service-fail" = {
+        serviceConfig = {
+          Type = "oneshot";
+          RemainAfterExit = true;
+          ExecStart = lib.getExe pkgs.bash;
+        };
+      };
     };
 
   testScript = ''
@@ -92,6 +105,8 @@ testPkgs.testers.runNixOSTest {
 
     machine.succeed("zfs create -o mountpoint=/mnt/rpool2_data rpool2/data")
 
+    machine.succeed("zfs create -o mountpoint=/mnt/rpool_moar_data rpool/moar_data")
+
     # Test that valid service starts successfully
     machine.succeed("systemctl start test-service")
 
@@ -117,6 +132,21 @@ testPkgs.testers.runNixOSTest {
     assert "Expected pool: rpool2" in journal_output
     assert "Actual pool:   rpool" in journal_output
 
+
+    # Test that invalid-service mount service fails validation
+    machine.fail("systemctl start multi-service-fail.service")
+
+    # Check the journal for our detailed validation error message
+    journal_output = machine.succeed("journalctl -u multi-service-fail-mounts.service --no-pager")
+    print("JOURNAL OUTPUT:")
+    print(journal_output)
+
+    # Verify our validation error is in the journal using Python string matching
+    assert "ERROR: ZFS pool mismatch for /mnt/rpool_moar_data" in journal_output, "no zfs pool mismatch found (1)"
+    assert "Expected pool: rpool2" in journal_output, "no zfs pool mismatch found (2)"
+    assert "Actual pool:   rpool" in journal_output, "no zfs pool mismatch found (3)"
+
+
     machine.succeed("systemctl start multi-service")
     machine.succeed("systemctl is-active multi-service-mounts.service")
   '';