diff --git a/testsuite/drivers/base_driver.py b/testsuite/drivers/base_driver.py
index c95e5ad2c..cb4896690 100644
--- a/testsuite/drivers/base_driver.py
+++ b/testsuite/drivers/base_driver.py
@@ -137,7 +137,8 @@ def baseline(self) -> tuple[str, str, bool]:
     @property
     def test_control_creator(self):
         return YAMLTestControlCreator({
-            'mode': self.env.options.mode
+            'mode': self.env.options.mode,
+            'os': self.env.build.os.name,
         })
 
     def set_up(self) -> None:
diff --git a/testsuite/drivers/gnatcheck_driver.py b/testsuite/drivers/gnatcheck_driver.py
index e6eda25bb..751d18eb4 100644
--- a/testsuite/drivers/gnatcheck_driver.py
+++ b/testsuite/drivers/gnatcheck_driver.py
@@ -1,6 +1,7 @@
 import os
 import os.path as P
 import re
+import sys
 import xml.etree.ElementTree as ET
 
 from e3.testsuite.driver.diff import (
@@ -173,7 +174,19 @@ def run(self) -> None:
         gnatcheck_env["LKQL_RULES_PATH"] = getattr(
             self.env, "gnatcheck_rules_path", ""
         )
+
+        # Get the test provided custom GNATcheck worker
         custom_worker = self.test_env.get('worker', None)
+
+        # Special case if the provided worker is "unparsable_generator" then
+        # we call the lkql_jit.py script in a special mode.
+        if custom_worker == "unparsable_generator":
+            custom_worker = " ".join([
+                sys.executable,
+                P.join(self.env.support_dir, "lkql_jit.py"),
+                "unparsable_generator"
+            ])
+
         gnatcheck_env["GNATCHECK_WORKER"] = custom_worker or " ".join(
             self.gnatcheck_worker_exe
         )
diff --git a/testsuite/python_support/lkql_jit.py b/testsuite/python_support/lkql_jit.py
index 20f45ed0e..1176f6522 100644
--- a/testsuite/python_support/lkql_jit.py
+++ b/testsuite/python_support/lkql_jit.py
@@ -58,18 +58,31 @@ def get_java_command(entry_point: str) -> list[str]:
         f'com.adacore.lkql_jit.{main_classes[entry_point]}'
     ]
 
+def print_gnatcheck_unparsable():
+    print("This line is not parsable")
+    print("Message: should appear")
+    print("no_a_file.adb:01:01: Message: Should not appear")
+    print("This line is not parsable either")
+
 if __name__ == '__main__':
     # Create the script argument parser
     parser = argparse.ArgumentParser(prog="lkql_jit.py",
                                      description=__doc__)
     subparsers = parser.add_subparsers(help="LKQL JIT entry point", required=True)
     for subcommand, help in [
-        ("lkql", "Main entry point for LKQL")
+        ("lkql", "Main entry point for LKQL"),
+        (
+            "unparsable_generator",
+            "Entry point to generate unparsable GNATcheck messages"
+        )
     ]:
         subp = subparsers.add_parser(subcommand, help=help)
         subp.set_defaults(subc=subcommand)
 
     args, to_forward = parser.parse_known_args()
-    command = get_java_command(args.subc)
-    command.extend(to_forward)
-    subprocess.run(command)
+    if args.subc == "unparsable_generator":
+        print_gnatcheck_unparsable()
+    else:
+        command = get_java_command(args.subc)
+        command.extend(to_forward)
+        subprocess.run(command)
diff --git a/testsuite/tests/gnatcheck_errors/invalid_worker/test.out b/testsuite/tests/gnatcheck_errors/invalid_worker/test.out
deleted file mode 100644
index ad5cd3fb7..000000000
--- a/testsuite/tests/gnatcheck_errors/invalid_worker/test.out
+++ /dev/null
@@ -1,3 +0,0 @@
-gnatcheck: Unparsable line: Not a message
-gnatcheck: Unparsable line: Message: Should appear
-gnatcheck: Unparsable line:  --files-from=/gnatcheck-files1.TMP --rules-from=/gnatcheck-rules0.TMP
diff --git a/testsuite/tests/gnatcheck_errors/invalid_worker/test.yaml b/testsuite/tests/gnatcheck_errors/invalid_worker/test.yaml
deleted file mode 100644
index 5c8444b92..000000000
--- a/testsuite/tests/gnatcheck_errors/invalid_worker/test.yaml
+++ /dev/null
@@ -1,7 +0,0 @@
-driver: gnatcheck
-format: brief
-worker: "echo Not a message\nnot_a_file.adb:01:01: Should not appear\nMessage: Should appear\n"
-input_sources:
-  - main.adb
-rules:
-  - +RGOTO_Statements
diff --git a/testsuite/tests/gnatcheck_errors/missing_source_dirs/prj.gpr b/testsuite/tests/gnatcheck_errors/missing_source_dirs/linux/prj.gpr
similarity index 100%
rename from testsuite/tests/gnatcheck_errors/missing_source_dirs/prj.gpr
rename to testsuite/tests/gnatcheck_errors/missing_source_dirs/linux/prj.gpr
diff --git a/testsuite/tests/gnatcheck_errors/missing_source_dirs/test.out b/testsuite/tests/gnatcheck_errors/missing_source_dirs/linux/test.out
similarity index 100%
rename from testsuite/tests/gnatcheck_errors/missing_source_dirs/test.out
rename to testsuite/tests/gnatcheck_errors/missing_source_dirs/linux/test.out
diff --git a/testsuite/tests/gnatcheck_errors/missing_source_dirs/linux/test.yaml b/testsuite/tests/gnatcheck_errors/missing_source_dirs/linux/test.yaml
new file mode 100644
index 000000000..8767e7adc
--- /dev/null
+++ b/testsuite/tests/gnatcheck_errors/missing_source_dirs/linux/test.yaml
@@ -0,0 +1,9 @@
+driver: gnatcheck
+format: brief
+project: prj.gpr
+rules:
+  - +RGOTO_Statements
+control:
+  - [SKIP,
+     "os == 'windows'",
+     "Disable this test on Windows due to path formatting"]
diff --git a/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/prj.gpr b/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/prj.gpr
new file mode 100644
index 000000000..a6fe033af
--- /dev/null
+++ b/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/prj.gpr
@@ -0,0 +1,3 @@
+project Prj is
+    for Source_Dirs use ("invalid_source_dirs");
+end Prj;
diff --git a/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/test.out b/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/test.out
new file mode 100644
index 000000000..f86df2c1c
--- /dev/null
+++ b/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/test.out
@@ -0,0 +1,4 @@
+gnatcheck: prj.gpr:2:26: error: "\invalid_source_dirs" is not a valid directory
+gnatcheck: prj.gpr: warning: there are no sources of language "Ada" in this project
+try "gnatcheck --help" for more information.
+>>>program returned status code 2
diff --git a/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/test.yaml b/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/test.yaml
new file mode 100644
index 000000000..2b232a09a
--- /dev/null
+++ b/testsuite/tests/gnatcheck_errors/missing_source_dirs/windows/test.yaml
@@ -0,0 +1,9 @@
+driver: gnatcheck
+format: brief
+project: prj.gpr
+rules:
+  - +RGOTO_Statements
+control:
+  - [SKIP,
+     "os != 'windows'",
+     "Disable this test on non-Windows systems due to path formatting"]
diff --git a/testsuite/tests/gnatcheck_errors/invalid_worker/main.adb b/testsuite/tests/gnatcheck_errors/unparsable_worker_messages/main.adb
similarity index 100%
rename from testsuite/tests/gnatcheck_errors/invalid_worker/main.adb
rename to testsuite/tests/gnatcheck_errors/unparsable_worker_messages/main.adb
diff --git a/testsuite/tests/gnatcheck_errors/unparsable_worker_messages/test.out b/testsuite/tests/gnatcheck_errors/unparsable_worker_messages/test.out
new file mode 100644
index 000000000..6b5dbdc2d
--- /dev/null
+++ b/testsuite/tests/gnatcheck_errors/unparsable_worker_messages/test.out
@@ -0,0 +1,3 @@
+gnatcheck: Unparsable line: This line is not parsable
+gnatcheck: Unparsable line: Message: should appear
+gnatcheck: Unparsable line: This line is not parsable either
diff --git a/testsuite/tests/gnatcheck_errors/missing_source_dirs/test.yaml b/testsuite/tests/gnatcheck_errors/unparsable_worker_messages/test.yaml
similarity index 50%
rename from testsuite/tests/gnatcheck_errors/missing_source_dirs/test.yaml
rename to testsuite/tests/gnatcheck_errors/unparsable_worker_messages/test.yaml
index dd920e401..b3f3b9779 100644
--- a/testsuite/tests/gnatcheck_errors/missing_source_dirs/test.yaml
+++ b/testsuite/tests/gnatcheck_errors/unparsable_worker_messages/test.yaml
@@ -1,5 +1,7 @@
 driver: gnatcheck
 format: brief
-project: prj.gpr
+worker: "unparsable_generator"
+input_sources:
+  - main.adb
 rules:
   - +RGOTO_Statements