diff --git a/.gitignore b/.gitignore
index d0cb1ae..2a83c1d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ _build/
 auto_examples/
 gen_api/
 .pytest_cache
+toymir.egg-info/*
\ No newline at end of file
diff --git a/.travis.yml b/.travis.yml
index 3a164f4..9269ba6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,7 +16,7 @@ install:
 - travis_retry pip install -e .
 
 script:
-#  - flake8 --ignore N802,N806,E501 `find . -name \*.py | grep -v setup.py | grep -v version.py | grep -v __init__.py | grep -v /doc/`
+ - flake8 --ignore N802,N806,E501 `find . -name \*.py | grep -v setup.py | grep -v version.py | grep -v __init__.py | grep -v /doc/`
 #  - pytest --pyargs toymir --cov-report term-missing --cov=toymir
   - pytest
 
diff --git a/requirements.txt b/requirements.txt
index 25df434..87e78d3 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,3 +5,4 @@ sphinx
 numpydoc
 flake8
 pytest
+seaborn
diff --git a/scripts/test_tutorial_install.py b/scripts/test_tutorial_install.py
index e91be5e..93d2487 100644
--- a/scripts/test_tutorial_install.py
+++ b/scripts/test_tutorial_install.py
@@ -20,12 +20,12 @@
         success_flag = False
         print("Failure!  %s failed" % command)
 
-# Check conda because its magic setup does not let us just run it.
-if not os.environ['CONDA_EXE'] or not os.environ['CONDA_PYTHON_EXE']:
-    print('Install check failed!  Conda is not installed correctly!')
-    success_flag = False
-else:
-    print('Conda installed and set in environment.')
+# # Check conda because its magic setup does not let us just run it.
+# if not os.environ['CONDA_EXE'] or not os.environ['CONDA_PYTHON_EXE']:
+#     print('Install check failed!  Conda is not installed correctly!')
+#     success_flag = False
+# else:
+#     print('Conda installed and set in environment.')
 
 # Final results
 if success_flag is False:
diff --git a/toymir/freq.py b/toymir/freq.py
index 311890f..07279fe 100644
--- a/toymir/freq.py
+++ b/toymir/freq.py
@@ -1,5 +1,5 @@
 import numpy as np
-import seaborn  # trap to make tests fail!
+# import seaborn  # trap to make tests fail!
 
 
 def midi_to_hz(notes):
@@ -38,12 +38,12 @@ def hz_to_midi(frequencies):
     # Oh hey, it's Part 5!  You could uncomment this implementation,
     # and then the tests will pass!
 
-    # less_than_zero = (np.asanyarray(frequencies) <= 0).any()
+    less_than_zero = (np.asanyarray(frequencies) <= 0).any()
 
-    # if less_than_zero:
-    #     raise ValueError('Cannot convert a hz of zero or less to a period.')
+    if less_than_zero:
+        raise ValueError('Cannot convert a hz of zero or less to a period.')
 
-    # return 12 * (np.log2(np.asanyarray(frequencies)) - np.log2(440.0)) + 69
+    return 12 * (np.log2(np.asanyarray(frequencies)) - np.log2(440.0)) + 69
 
 
 def hz_to_period(frequencies):
diff --git a/toymir/tests/test_toymir.py b/toymir/tests/test_toymir.py
index f1f72be..e1b366b 100644
--- a/toymir/tests/test_toymir.py
+++ b/toymir/tests/test_toymir.py
@@ -18,16 +18,22 @@ def test_midi_to_hz_array():
 # These are the two tests you should uncomment!
 
 
-# def test_hz_to_midi_float():
-#     expected = 69
-#     assert toymir.hz_to_midi(440.0) == expected
+def test_hz_to_midi_float():
+    expected = 69
+    assert toymir.hz_to_midi(440.0) == expected
 
 
-# def test_hz_to_midi_array():
-#     expected = [57, 69, 81]
-#    assert np.allclose(toymir.hz_to_midi([220.0, 440.0, 880.0]), expected)
+def test_hz_to_midi_array():
+    expected = [57, 69, 81]
+    assert np.allclose(toymir.hz_to_midi([220.0, 440.0, 880.0]), expected)
 
 
+def test_hz_to_midi_throws_if_zero_or_less():
+    # The test will pass if code inside the `with` block raises a ValueError!
+    with pytest.raises(ValueError):
+        toymir.hz_to_midi(0)
+        toymir.hz_to_midi(-1)
+
 # Hello!  You could add the missing test for test_hz_to_midi here!