diff --git a/py_wake/tests/notebook.py b/py_wake/tests/notebook.py
index 9259fe3adf95167ac08396dd21ac78b91249f026..1f730a40c0bb14117f1db41ab622ceeb4067b18e 100644
--- a/py_wake/tests/notebook.py
+++ b/py_wake/tests/notebook.py
@@ -6,9 +6,16 @@ import re
 import ssl
 import sys
 import matplotlib.pyplot as plt
+from _io import StringIO
 
 
 class Notebook():
+    pip_header = """# Install PyWake if needed
+try:
+    import py_wake
+except ModuleNotFoundError:
+    !pip install git+https://gitlab.windenergy.dtu.dk/TOPFARM/PyWake.git"""
+
     def __init__(self, filename):
         self.filename = filename
         try:
@@ -99,8 +106,8 @@ class Notebook():
         try:
             import contextlib
 
-            with contextlib.redirect_stdout(None):
-                with contextlib.redirect_stderr(None):
+            with contextlib.redirect_stdout(StringIO()):
+                with contextlib.redirect_stderr(StringIO()):
                     exec("def test():\n    " + "\n    ".join(lines) + "\ntest()", {}, {})
                     plt.close()
         except Exception as e:
@@ -130,19 +137,15 @@ class Notebook():
         # print(txt)
 
     def check_pip_header(self):
-        pip_header = """# Install PyWake if needed
-try:
-    import py_wake
-except ModuleNotFoundError:
-    !pip install git+https://gitlab.windenergy.dtu.dk/TOPFARM/PyWake.git"""
+
         code = self.get_code()
         if not code:
             return
-        if code[0].strip() != pip_header:
+        if code[0].strip() != self.pip_header:
             for i, cell in enumerate(self.cells):
                 if cell['cell_type'] == "code":
                     break
-            self.insert_code_cell(i, pip_header)
+            self.insert_code_cell(i, self.pip_header)
             self.save()
             raise Exception("""pip install header was not present in %s.
 It has now been auto insert. Please check the notebook and commit the changes""" % os.path.abspath(self.filename))
diff --git a/py_wake/tests/test_wind_farm_models/test_enginering_wind_farm_model.py b/py_wake/tests/test_wind_farm_models/test_enginering_wind_farm_model.py
index 47f72d8a75efb8f0985b62191838a43df928a1f0..2562314a3d4ac5372d5b4dda72b6ec0d5eac52dc 100644
--- a/py_wake/tests/test_wind_farm_models/test_enginering_wind_farm_model.py
+++ b/py_wake/tests/test_wind_farm_models/test_enginering_wind_farm_model.py
@@ -241,3 +241,16 @@ def test_double_wind_farm_model():
     PropagateDownwind(site, windTurbines, wake_deficitModel=NoWakeDeficit())
     aep = wfm(x, y).aep().sum()
     npt.assert_array_equal(aep, aep_ref)
+
+
+def test_double_wind_farm_model_All2AllIterative():
+    """Check that a new wind farm model does not change results of previous"""
+    site = IEA37Site(64)
+    x, y = site.initial_position.T
+    x, y = wt_x, wt_y
+    windTurbines = IEA37_WindTurbines()
+    wfm = All2AllIterative(site, windTurbines, wake_deficitModel=IEA37SimpleBastankhahGaussianDeficit())
+    aep_ref = wfm(x, y).aep().sum()
+    All2AllIterative(site, windTurbines, wake_deficitModel=NoWakeDeficit())(x, y)
+    aep = wfm(x, y).aep().sum()
+    npt.assert_array_equal(aep, aep_ref)
diff --git a/py_wake/utils/progressbar.py b/py_wake/utils/progressbar.py
index a14332172bc6974689a5bbdb2d98dc5791be417d..b51b9f545680869273e95ff3bd85779c2aa5dd7e 100644
--- a/py_wake/utils/progressbar.py
+++ b/py_wake/utils/progressbar.py
@@ -1,11 +1,8 @@
 
 def progressbar(it, show=True):
     if show and len(it) > 1:
-        try:
-            from tqdm import tqdm
-            return tqdm(it)
-        except Exception:
-            return it
+        from tqdm import tqdm
+        return tqdm(it)
     else:
         return it