diff --git a/catinabox/catactivities.py b/catinabox/catactivities.py
index 012367b..34a53b1 100644
--- a/catinabox/catactivities.py
+++ b/catinabox/catactivities.py
@@ -20,3 +20,5 @@ def cat_nap(nap_seconds):
     if nap_seconds < LENGTH_OF_SATISFYING_NAP:
         raise NapWillNotBeSatisfying(nap_seconds)
     time.sleep(nap_seconds)
+
+#nothing
diff --git a/tests/test_catactivities.py b/tests/test_catactivities.py
index e2051b1..ef82ac1 100644
--- a/tests/test_catactivities.py
+++ b/tests/test_catactivities.py
@@ -1,14 +1,25 @@
-# import pytest
-# import time
+import pytest
+import time
 
-# from catinabox import catactivities
+# why not necessary: ?
+# from pytest_mock import mocker
+
+from catinabox import catactivities
 
 
 def test__cat_nap__satisfying_nap(mocker):
-    # mock_sleep = mocker.patch.object(time, "sleep", autospec=True)
-    assert True
+    mock_sleep = mocker.patch.object(time, "sleep", autospec=True)
+    # how to test: test for called_with value:
+    # mock_sleep.return_value = 20
+    # assert mock_sleep.called_with(20*60)
+    # assert mock_sleep.call_args(20*60)
+    catactivities.cat_nap(20*60)
+    mock_sleep.assert_called_with(20*60)
 
 
 def test__cat_nap__not_satisfying(mocker):
-    # mock_sleep = mocker.patch.object(time, "sleep", autospec=True)
-    assert True
+    mock_sleep = mocker.patch.object(time, "sleep", autospec=True)
+    # mock_sleep.called_with(4*60)
+    with pytest.raises(catactivities.NapWillNotBeSatisfying):
+        catactivities.cat_nap(4*60)  # too short!
+    assert mock_sleep.call_count == 0
diff --git a/tests/test_catmath.py b/tests/test_catmath.py
index ced6358..233388c 100644
--- a/tests/test_catmath.py
+++ b/tests/test_catmath.py
@@ -2,15 +2,15 @@
 
 
 def test__cat_years_to_hooman_years__middle_age__succeeds():
-    assert True
+    assert catmath.cat_years_to_hooman_years(8) == 40
 
 
 def test__cat_years_to_hooman_years__less_than_one_year__succeeds():
-    assert True
+    assert catmath.cat_years_to_hooman_years(0.75) == 3.75
 
 
 def test__cat_years_to_hooman_years__0__returns_0():
-    assert True
+    assert catmath.cat_years_to_hooman_years(0) == 0
 
 
 # BONUS MATERIAL FOR STEP 2
diff --git a/tests/test_cattery.py b/tests/test_cattery.py
index b36692c..527c38c 100644
--- a/tests/test_cattery.py
+++ b/tests/test_cattery.py
@@ -7,33 +7,34 @@
 # add_cats
 ###########################################################################
 
-def test__add_cats__succeeds():
-    c = cattery.Cattery()
-    c.add_cats(["Fluffy", "Snookums"])
-    assert c.cats == ["Fluffy", "Snookums"]
-    assert c.num_cats == 2
+@pytest.fixture()
+def cattery_client():
+    return cattery.Cattery()
+
+
+def test__add_cats__succeeds(cattery_client):
+    cattery_client.add_cats(["Fluffy", "Snookums"])
+    assert cattery_client.cats == ["Fluffy", "Snookums"]
+    assert cattery_client.num_cats == 2
 
 
 ###########################################################################
 # remove_cat
 ###########################################################################
 
-def test__remove_cat__succeeds():
-    c = cattery.Cattery()
-    c.add_cats(["Fluffy", "Junior"])
-    c.remove_cat("Fluffy")
-    assert c.cats == ["Junior"]
-    assert c.num_cats == 1
+def test__remove_cat__succeeds(cattery_client):
+    cattery_client.add_cats(["Fluffy", "Junior"])
+    cattery_client.remove_cat("Fluffy")
+    assert cattery_client.cats == ["Junior"]
+    assert cattery_client.num_cats == 1
 
 
-def test__remove_cat__no_cats__fails():
-    c = cattery.Cattery()
+def test__remove_cat__no_cats__fails(cattery_client):
     with pytest.raises(cattery.CatNotFound):
-        c.remove_cat("Fluffles")
+        cattery_client.remove_cat("Fluffles")
 
 
-def test__remove_cat__cat_not_in_cattery__fails():
-    c = cattery.Cattery()
-    c.add_cats(["Fluffy"])
+def test__remove_cat__cat_not_in_cattery__fails(cattery_client):
+    cattery_client.add_cats(["Fluffy"])
     with pytest.raises(cattery.CatNotFound):
-        c.remove_cat("Snookums")
+        cattery_client.remove_cat("Snookums")
diff --git a/tests/test_safecatmath.py b/tests/test_safecatmath.py
index 3f85a35..fd26197 100644
--- a/tests/test_safecatmath.py
+++ b/tests/test_safecatmath.py
@@ -1,4 +1,4 @@
-# import pytest
+import pytest
 
 from catinabox import safecatmath
 
@@ -19,17 +19,20 @@ def test__cat_years_to_hooman_years__0__returns_0():
 
 
 def test__cat_years_to_hooman_years__less_0__raises():
-    assert True
+    with pytest.raises(safecatmath.InvalidAge):
+        safecatmath.cat_years_to_hooman_years(-3)
 
 
 def test__cat_years_to_hooman_years__older_than_1000__raises():
-    assert True
+    with pytest.raises(safecatmath.InvalidAge):
+        safecatmath.cat_years_to_hooman_years(1100)
 
 
 def test__cat_years_to_hooman_years__string__raises():
-    assert True
+    with pytest.raises(safecatmath.InvalidAge):
+        safecatmath.cat_years_to_hooman_years('11')
 
 
 def test__cat_years_to_hooman_years__nan__raises():
-    # hooman_age = float('nan')
-    assert True
+    with pytest.raises(safecatmath.InvalidAge):
+        safecatmath.cat_years_to_hooman_years(float('nan'))