diff --git a/.travis.yml b/.travis.yml
index 3a164f4..0d56779 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,9 +16,9 @@ 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/`
-#  - pytest --pyargs toymir --cov-report term-missing --cov=toymir
-  - pytest
+- 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
 
 # Hey, this block (and the above arguments to pytest )
 # are important if you care about test coverage.
diff --git a/requirements.txt b/requirements.txt
index 25df434..71c333d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,3 +5,4 @@ sphinx
 numpydoc
 flake8
 pytest
+seaborn 
diff --git a/toymir/__init__.py b/toymir/__init__.py
index ad625cc..4922376 100644
--- a/toymir/__init__.py
+++ b/toymir/__init__.py
@@ -2,4 +2,4 @@
 # When you import from .MODULE, that means look within the current package
 # instead of going out to the installed packages
 from .version import __version__  # noqa
-from .freq import *  # noqa
+from .freq import * # noqa
diff --git a/toymir/freq.py b/toymir/freq.py
index 311890f..338076f 100644
--- a/toymir/freq.py
+++ b/toymir/freq.py
@@ -1,9 +1,25 @@
 import numpy as np
-import seaborn  # trap to make tests fail!
+# import seaborn trap to make tests fail!
 
 
 def midi_to_hz(notes):
-    """Hello Part 6!  You should add documentation to this function.
+    """Get frequencies (Hz) of MIDI
+
+    Parameters
+    ----------
+    notes         :  number or np.ndarray [shape=(n,), dtype=float]
+        note numbers to convert
+
+    Returns
+    -------
+
+    frequences    : float or np.ndarray [shape=(n,), dtype=float]
+        frequences to convert
+
+    Examples
+    --------
+    >>> midi_to_hz(120)
+    8372.01
     """
 
     return 440.0 * (2.0 ** ((np.asanyarray(notes) - 69.0) / 12.0))
@@ -38,12 +54,12 @@ 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..321835a 100644
--- a/toymir/tests/test_toymir.py
+++ b/toymir/tests/test_toymir.py
@@ -18,17 +18,17 @@ 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)
 
 
-# Hello!  You could add the missing test for test_hz_to_midi here!
+# Hello! You could add the missing test for test_hz_to_midi here!
 
 
 def test_hz_to_period_float():