diff --git a/src/data_handling/bootstraps.py b/src/data_handling/bootstraps.py
index 21fc23d8a072867dbd28b2ede7255325db206164..2700cb6c0aaff7227bfea78116a5417aeae9b201 100644
--- a/src/data_handling/bootstraps.py
+++ b/src/data_handling/bootstraps.py
@@ -25,7 +25,7 @@ class BootStraps(RunEnvironment):
         variables_str = '_'.join(sorted(self.test_data.variables))
         window = self.test_data.window_history_size
         for station in self.test_data.stations:
-            valid, _, max_nboot = self.valid_bootstrap_file(station, variables_str, window)
+            valid, max_nboot = self.valid_bootstrap_file(station, variables_str, window)
             if not valid:
                 logging.info(f'create bootstap data for {station}')
                 hist, _ = self.test_data[station]
@@ -44,23 +44,17 @@ class BootStraps(RunEnvironment):
         str_re = re.compile(f"{station}_{variables}_hist(\d+)_nboots(\d+)_shuffled*")
         dir_list = os.listdir(self.bootstrap_path)
         max_nboot = self.number_bootstraps
-        max_window = self.number_bootstraps
         for file in dir_list:
             match = str_re.match(file)
             if match:
                 window_existing = int(match.group(1))
                 nboot_existing = int(match.group(2))
-                max_window = max([max_window, window_existing])
                 max_nboot = max([max_nboot, nboot_existing])
                 if (window_existing >= window) and (nboot_existing >= self.number_bootstraps):
-                    return True, 0, 0
+                    return True, None
                 else:
                     os.remove(os.path.join(self.bootstrap_path, file))
-        return False, max_window, max_nboot
-
-
-
-
+        return False, max_nboot
 
     def shuffle_single_variable(self, data):
         orig_shape = data.shape
@@ -69,7 +63,6 @@ class BootStraps(RunEnvironment):
         return np.random.choice(data.reshape(-1,), size=size)
 
 
-
 if __name__ == "__main__":
 
     from src.run_modules.experiment_setup import ExperimentSetup
diff --git a/test/test_data_handling/test_bootstraps.py b/test/test_data_handling/test_bootstraps.py
new file mode 100644
index 0000000000000000000000000000000000000000..ed572161e535cc24332a76f4cbce86403eb1d067
--- /dev/null
+++ b/test/test_data_handling/test_bootstraps.py
@@ -0,0 +1,46 @@
+
+from src.data_handling.bootstraps import BootStraps
+
+import pytest
+import os
+
+
+class TestBootstraps:
+
+    @pytest.fixture
+    def boot_no_init(self):
+        obj = object.__new__(BootStraps)
+        super(BootStraps, obj).__init__()
+        obj.number_bootstraps = 50
+        return obj
+
+    def test_valid_bootstrap_file(self, boot_no_init):
+        path = os.path.join(os.path.dirname(__file__), "data")
+        os.makedirs(path)
+        boot_no_init.bootstrap_path = path
+        station = "TESTSTATION"
+        variables = "var1_var2_var3"
+        window = 5
+        # empty case
+        assert len(os.listdir(path)) == 0
+        assert boot_no_init.valid_bootstrap_file(station, variables, window) == (False, 50)
+        # different cases, where files with bigger range are existing
+        os.mknod(os.path.join(path, f"{station}_{variables}_hist5_nboots50_shuffled.dat"))
+        assert boot_no_init.valid_bootstrap_file(station, variables, window) == (True, None)
+        os.mknod(os.path.join(path, f"{station}_{variables}_hist5_nboots100_shuffled.dat"))
+        assert boot_no_init.valid_bootstrap_file(station, variables, window) == (True, None)
+        os.mknod(os.path.join(path, f"{station}_{variables}_hist10_nboots50_shuffled.dat"))
+        os.mknod(os.path.join(path, f"{station}1_{variables}_hist10_nboots50_shuffled.dat"))
+        assert boot_no_init.valid_bootstrap_file(station, variables, window) == (True, None)
+        #  need to reload data and therefore remove not fitting files for this station
+        assert boot_no_init.valid_bootstrap_file(station, variables, 20) == (False, 100)
+        assert len(os.listdir(path)) == 1
+        # reload because expanded boot number
+        os.mknod(os.path.join(path, f"{station}_{variables}_hist5_nboots50_shuffled.dat"))
+        boot_no_init.number_bootstraps = 60
+        assert boot_no_init.valid_bootstrap_file(station, variables, window) == (False, 60)
+        assert len(os.listdir(path)) == 1
+        # reload because of expanded window size, but use maximum boot number from file names
+        os.mknod(os.path.join(path, f"{station}_{variables}_hist5_nboots60_shuffled.dat"))
+        boot_no_init.number_bootstraps = 50
+        assert boot_no_init.valid_bootstrap_file(station, variables, 20) == (False, 60)