diff --git a/OMPython/ModelicaSystem.py b/OMPython/ModelicaSystem.py
index ccec499b..1a979647 100644
--- a/OMPython/ModelicaSystem.py
+++ b/OMPython/ModelicaSystem.py
@@ -2276,12 +2276,12 @@ def get_doe_solutions(
                 continue
 
             if var_list is None:
-                var_list_row = list(self._mod.getSolutions(resultfile=resultfile.as_posix()))
+                var_list_row = list(self._mod.getSolutions(resultfile=resultfile))
             else:
                 var_list_row = var_list
 
             try:
-                sol = self._mod.getSolutions(varList=var_list_row, resultfile=resultfile.as_posix())
+                sol = self._mod.getSolutions(varList=var_list_row, resultfile=resultfile)
                 sol_data = {var: sol[idx] for idx, var in enumerate(var_list_row)}
                 sol_dict[resultfilename]['msg'] = 'Simulation available'
                 sol_dict[resultfilename]['data'] = sol_data
diff --git a/tests/test_FMIImport.py b/tests/test_FMIImport.py
index 44249f5c..cb43e0ae 100644
--- a/tests/test_FMIImport.py
+++ b/tests/test_FMIImport.py
@@ -21,11 +21,12 @@ def model_firstorder(tmp_path):
 
 
 def test_FMIImport(model_firstorder):
-    filePath = model_firstorder.as_posix()
-
     # create model & simulate it
     mod1 = OMPython.ModelicaSystem()
-    mod1.model(model_file=filePath, model_name="M")
+    mod1.model(
+        model_file=model_firstorder,
+        model_name="M",
+    )
     mod1.simulate()
 
     # create FMU & check
diff --git a/tests/test_ModelicaSystem.py b/tests/test_ModelicaSystem.py
index f49fb20c..8567c426 100644
--- a/tests/test_ModelicaSystem.py
+++ b/tests/test_ModelicaSystem.py
@@ -40,10 +40,9 @@ def model_firstorder(tmp_path, model_firstorder_content):
 
 def test_ModelicaSystem_loop(model_firstorder):
     def worker():
-        filePath = model_firstorder.as_posix()
         mod = OMPython.ModelicaSystem()
         mod.model(
-            model_file=filePath,
+            model_file=model_firstorder,
             model_name="M",
         )
         mod.simulate()
@@ -139,12 +138,11 @@ def test_relative_path(model_firstorder):
 
 
 def test_customBuildDirectory(tmp_path, model_firstorder):
-    filePath = model_firstorder.as_posix()
     tmpdir = tmp_path / "tmpdir1"
     tmpdir.mkdir()
     mod = OMPython.ModelicaSystem(work_directory=tmpdir)
     mod.model(
-        model_file=filePath,
+        model_file=model_firstorder,
         model_name="M",
     )
     assert pathlib.Path(mod.getWorkDirectory()).resolve() == tmpdir.resolve()
@@ -222,7 +220,7 @@ def test_getters(tmp_path):
 """)
     mod = OMPython.ModelicaSystem()
     mod.model(
-        model_file=model_file.as_posix(),
+        model_file=model_file,
         model_name="M_getters",
     )
 
@@ -418,7 +416,7 @@ def test_simulate_inputs(tmp_path):
 """)
     mod = OMPython.ModelicaSystem()
     mod.model(
-        model_file=model_file.as_posix(),
+        model_file=model_file,
         model_name="M_input",
     )
 
diff --git a/tests/test_ModelicaSystemCmd.py b/tests/test_ModelicaSystemCmd.py
index d736d5ca..7eaf08ba 100644
--- a/tests/test_ModelicaSystemCmd.py
+++ b/tests/test_ModelicaSystemCmd.py
@@ -20,7 +20,7 @@ def model_firstorder(tmp_path):
 def mscmd_firstorder(model_firstorder):
     mod = OMPython.ModelicaSystem()
     mod.model(
-        model_file=model_firstorder.as_posix(),
+        model_file=model_firstorder,
         model_name="M",
     )
     mscmd = OMPython.ModelicaSystemCmd(
diff --git a/tests/test_ModelicaSystemDoE.py b/tests/test_ModelicaSystemDoE.py
index d290c715..f9d70011 100644
--- a/tests/test_ModelicaSystemDoE.py
+++ b/tests/test_ModelicaSystemDoE.py
@@ -56,7 +56,7 @@ def test_ModelicaSystemDoE_local(tmp_path, model_doe, param_doe):
     tmpdir.mkdir(exist_ok=True)
 
     doe_mod = OMPython.ModelicaSystemDoE(
-        model_file=model_doe.as_posix(),
+        model_file=model_doe,
         model_name="M",
         parameters=param_doe,
         resultpath=tmpdir,
@@ -74,7 +74,7 @@ def test_ModelicaSystemDoE_docker(tmp_path, model_doe, param_doe):
     assert omc.sendExpression("getVersion()") == "OpenModelica 1.25.0"
 
     doe_mod = OMPython.ModelicaSystemDoE(
-        model_file=model_doe.as_posix(),
+        model_file=model_doe,
         model_name="M",
         parameters=param_doe,
         omc_process=omcp,
@@ -91,7 +91,7 @@ def test_ModelicaSystemDoE_WSL(tmp_path, model_doe, param_doe):
     tmpdir.mkdir(exist_ok=True)
 
     doe_mod = OMPython.ModelicaSystemDoE(
-        model_file=model_doe.as_posix(),
+        model_file=model_doe,
         model_name="M",
         parameters=param_doe,
         resultpath=tmpdir,
diff --git a/tests/test_linearization.py b/tests/test_linearization.py
index ebfbc100..c61462bb 100644
--- a/tests/test_linearization.py
+++ b/tests/test_linearization.py
@@ -62,7 +62,7 @@ def test_getters(tmp_path):
 """)
     mod = OMPython.ModelicaSystem()
     mod.model(
-        model_file=model_file.as_posix(),
+        model_file=model_file,
         model_name="Pendulum",
         libraries=["Modelica"],
     )
diff --git a/tests/test_optimization.py b/tests/test_optimization.py
index 96c6fdbd..be6945f3 100644
--- a/tests/test_optimization.py
+++ b/tests/test_optimization.py
@@ -36,7 +36,7 @@ def test_optimization_example(tmp_path):
 
     mod = OMPython.ModelicaSystem()
     mod.model(
-        model_file=model_file.as_posix(),
+        model_file=model_file,
         model_name="BangBang2021",
     )
 
@@ -57,7 +57,10 @@ def test_optimization_example(tmp_path):
     # it is necessary to specify resultfile, otherwise it wouldn't find it.
     resultfile_str = r["resultFile"]
     resultfile_omcpath = mod.session().omcpath(resultfile_str)
-    time, f, v = mod.getSolutions(["time", "f", "v"], resultfile=resultfile_omcpath.as_posix())
+    time, f, v = mod.getSolutions(
+        varList=["time", "f", "v"],
+        resultfile=resultfile_omcpath,
+    )
     assert np.isclose(f[0], 10)
     assert np.isclose(f[-1], -10)