diff --git a/.travis.yml b/.travis.yml
index 12947e8..cc1355c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,4 @@
 language: python
-sudo: required
-dist: xenial
 group: travis_latest
 
 git:
@@ -8,22 +6,25 @@ git:
   quiet: true
 
 python:
+- 3.5
 - 3.6
-- 3.7
+- pypy3
 
 os:
 - linux
 
-install: pip install -e .[tests]
+install:
+- pip install -e .[tests]
+- if [[ $TRAVIS_PYTHON_VERSION == 3.6* && $TRAVIS_OS_NAME == linux  ]]; then pip install -e .[cov]; fi
 
 script:
 - pytest -rsv
-- flake8
-- mypy . --ignore-missing-imports
+- if [[ $TRAVIS_PYTHON_VERSION == 3.6* && $TRAVIS_OS_NAME == linux  ]]; then flake8; fi
+- if [[ $TRAVIS_PYTHON_VERSION == 3.6* && $TRAVIS_OS_NAME == linux  ]]; then mypy . --ignore-missing-imports; fi
 
 after_success:
-- if [[ $TRAVIS_PYTHON_VERSION == 3.6* ]]; then
-  pytest --cov;
+- if [[ $TRAVIS_PYTHON_VERSION == 3.6* && $TRAVIS_OS_NAME == linux ]]; then
+  pytest --cov --cov-config=setup.cfg;
   coveralls;
   fi
 
diff --git a/MANIFEST.in b/MANIFEST.in
index 1aba38f..065cc87 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1 +1,2 @@
 include LICENSE
+recursive-include tests *.py
diff --git a/README.md b/README.md
index a697169..4022df1 100644
--- a/README.md
+++ b/README.md
@@ -10,8 +10,7 @@
 # Science Dates & Times
 
 Date & time conversions used in the sciences. 
-The assumption is that datetimes are timezone-naive, as this will be required soon in Numpy *et al* for
-`numpy.datetime64`.
+The assumption is that datetimes are timezone-naive, as this is required in Numpy *et al* for `numpy.datetime64`.
 
 
 ## Install
diff --git a/date2doy.jl b/date2doy.jl
index 1c7a6d1..52fb17c 100755
--- a/date2doy.jl
+++ b/date2doy.jl
@@ -2,7 +2,7 @@
 #=
 command-line utility to convert date to day of year
 =#
-using Base.Dates
+using Dates
 using ArgParse
 
 
diff --git a/randomdate.jl b/randomdate.jl
index 12e6cee..c4ef162 100755
--- a/randomdate.jl
+++ b/randomdate.jl
@@ -4,21 +4,21 @@ generate a random date (month and day) in a year.
 Michael Hirsch, Ph.D.
 =#
 
-using Base.Dates
+using Dates
 using ArgParse
 
 function randomdate(year)
-    t = DateTime(year)
-    t += Day(rand(0:daysinyear(t)-1))
+  t = DateTime(year)
+  t += Day(rand(0:daysinyear(t)-1))
 end
 
 
 s = ArgParseSettings()
 @add_arg_table s begin
-    "year"
-        help = "year in which to generate a random date"
-        arg_type = Int
-        required = true
+  "year"
+    help = "year in which to generate a random date"
+    arg_type = Int
+    required = true
 end
 s = parse_args(s)
 
diff --git a/sciencedates/__init__.py b/sciencedates/__init__.py
index 29f5b1e..c2aa0d5 100644
--- a/sciencedates/__init__.py
+++ b/sciencedates/__init__.py
@@ -1,11 +1,15 @@
-from __future__ import division
 import datetime
-from pytz import UTC
 import numpy as np
 from dateutil.parser import parse
 import calendar
 import random
-from typing import Union, Tuple, Any, List
+from typing import Union, Tuple, List
+
+from .findnearest import find_nearest  # noqa: F401
+try:
+    from .tz import forceutc  # noqa: F401
+except ImportError:
+    pass
 
 
 def datetime2yeardoy(time: Union[str, datetime.datetime]) -> Tuple[int, float]:
@@ -17,7 +21,7 @@ def datetime2yeardoy(time: Union[str, datetime.datetime]) -> Tuple[int, float]:
     yd: yyyyddd four digit year, 3 digit day of year (INTEGER)
     utsec: seconds from midnight utc
     """
-    T: np.ndarray = np.atleast_1d(time)
+    T = np.atleast_1d(time)
 
     utsec = np.empty_like(T, float)
     yd = np.empty_like(T, int)
@@ -116,7 +120,7 @@ def datetime2gtd(time: Union[str, datetime.datetime, np.datetime64],
         elif isinstance(t, (datetime.datetime, datetime.date)):
             pass
         else:
-            raise TypeError(f'unknown time datatype {type(t)}')
+            raise TypeError('unknown time datatype {}'.format(type(t)))
 # %% Day of year
         doy[i] = int(t.strftime('%j'))
 # %% seconds since utc midnight
@@ -145,36 +149,6 @@ def datetime2utsec(t: Union[str, datetime.date, datetime.datetime, np.datetime64
                                                                           datetime.datetime.min.time()))
 
 
-def forceutc(t: Union[str, datetime.datetime, datetime.date, np.datetime64]) -> Union[datetime.datetime, datetime.date]:
-    """
-    Add UTC to datetime-naive and convert to UTC for datetime aware
-
-    input: python datetime (naive, utc, non-utc) or Numpy datetime64  #FIXME add Pandas and AstroPy time classes
-    output: utc datetime
-    """
-    # need to passthrough None for simpler external logic.
-# %% polymorph to datetime
-    if isinstance(t, str):
-        t = parse(t)
-    elif isinstance(t, np.datetime64):
-        t = t.astype(datetime.datetime)
-    elif isinstance(t, datetime.datetime):
-        pass
-    elif isinstance(t, datetime.date):
-        return t
-    elif isinstance(t, (np.ndarray, list, tuple)):
-        return np.asarray([forceutc(T) for T in t])
-    else:
-        raise TypeError('datetime only input')
-# %% enforce UTC on datetime
-    if t.tzinfo is None:  # datetime-naive
-        t = t.replace(tzinfo=UTC)
-    else:  # datetime-aware
-        t = t.astimezone(UTC)  # changes timezone, preserving absolute time. E.g. noon EST = 5PM UTC
-
-    return t
-
-
 def yeardec2datetime(atime: float) -> datetime.datetime:
     """
     Convert atime (a float) to DT.datetime
@@ -223,7 +197,7 @@ def datetime2yeardec(time: Union[str, datetime.datetime, datetime.date]) -> floa
     elif isinstance(time, (tuple, list, np.ndarray)):
         return np.asarray([datetime2yeardec(t) for t in time])
     else:
-        raise TypeError(f'unknown input type {type(time)}')
+        raise TypeError('unknown input type {}'.format(type(time)))
 
     year = t.year
 
@@ -233,46 +207,6 @@ def datetime2yeardec(time: Union[str, datetime.datetime, datetime.date]) -> floa
     return year + ((t - boy).total_seconds() / ((eoy - boy).total_seconds()))
 
 
-# %%
-def find_nearest(x, x0) -> Tuple[int, Any]:
-    """
-    This find_nearest function does NOT assume sorted input
-
-    inputs:
-    x: array (float, int, datetime, h5py.Dataset) within which to search for x0
-    x0: singleton or array of values to search for in x
-
-    outputs:
-    idx: index of flattened x nearest to x0  (i.e. works with higher than 1-D arrays also)
-    xidx: x[idx]
-
-    Observe how bisect.bisect() gives the incorrect result!
-
-    idea based on:
-    http://stackoverflow.com/questions/2566412/find-nearest-value-in-numpy-array
-
-    """
-    x = np.asanyarray(x)  # for indexing upon return
-    x0 = np.atleast_1d(x0)
-# %%
-    if x.size == 0 or x0.size == 0:
-        raise ValueError('empty input(s)')
-
-    if x0.ndim not in (0, 1):
-        raise ValueError('2-D x0 not handled yet')
-# %%
-    ind = np.empty_like(x0, dtype=int)
-
-    # NOTE: not trapping IndexError (all-nan) becaues returning None can surprise with slice indexing
-    for i, xi in enumerate(x0):
-        if xi is not None and (isinstance(xi, (datetime.datetime, datetime.date, np.datetime64)) or np.isfinite(xi)):
-            ind[i] = np.nanargmin(abs(x-xi))
-        else:
-            raise ValueError('x0 must NOT be None or NaN to avoid surprising None return value')
-
-    return ind.squeeze()[()], x[ind].squeeze()[()]   # [()] to pop scalar from 0d array while being OK with ndim>0
-
-
 def randomdate(year: int) -> datetime.date:
     """ gives random date in year"""
     if calendar.isleap(year):
diff --git a/sciencedates/findnearest.py b/sciencedates/findnearest.py
new file mode 100644
index 0000000..64cfa75
--- /dev/null
+++ b/sciencedates/findnearest.py
@@ -0,0 +1,42 @@
+from typing import Tuple, Any
+import numpy as np
+import datetime
+
+
+def find_nearest(x, x0) -> Tuple[int, Any]:
+    """
+    This find_nearest function does NOT assume sorted input
+
+    inputs:
+    x: array (float, int, datetime, h5py.Dataset) within which to search for x0
+    x0: singleton or array of values to search for in x
+
+    outputs:
+    idx: index of flattened x nearest to x0  (i.e. works with higher than 1-D arrays also)
+    xidx: x[idx]
+
+    Observe how bisect.bisect() gives the incorrect result!
+
+    idea based on:
+    http://stackoverflow.com/questions/2566412/find-nearest-value-in-numpy-array
+
+    """
+    x = np.asanyarray(x)  # for indexing upon return
+    x0 = np.atleast_1d(x0)
+# %%
+    if x.size == 0 or x0.size == 0:
+        raise ValueError('empty input(s)')
+
+    if x0.ndim not in (0, 1):
+        raise ValueError('2-D x0 not handled yet')
+# %%
+    ind = np.empty_like(x0, dtype=int)
+
+    # NOTE: not trapping IndexError (all-nan) becaues returning None can surprise with slice indexing
+    for i, xi in enumerate(x0):
+        if xi is not None and (isinstance(xi, (datetime.datetime, datetime.date, np.datetime64)) or np.isfinite(xi)):
+            ind[i] = np.nanargmin(abs(x-xi))
+        else:
+            raise ValueError('x0 must NOT be None or NaN to avoid surprising None return value')
+
+    return ind.squeeze()[()], x[ind].squeeze()[()]   # [()] to pop scalar from 0d array while being OK with ndim>0
diff --git a/sciencedates/tz.py b/sciencedates/tz.py
new file mode 100644
index 0000000..d45fb50
--- /dev/null
+++ b/sciencedates/tz.py
@@ -0,0 +1,35 @@
+from typing import Union
+import numpy as np
+import datetime
+from pytz import UTC
+from dateutil.parser import parse
+
+
+def forceutc(t: Union[str, datetime.datetime, datetime.date, np.datetime64]) -> Union[datetime.datetime, datetime.date]:
+    """
+    Add UTC to datetime-naive and convert to UTC for datetime aware
+
+    input: python datetime (naive, utc, non-utc) or Numpy datetime64  #FIXME add Pandas and AstroPy time classes
+    output: utc datetime
+    """
+    # need to passthrough None for simpler external logic.
+# %% polymorph to datetime
+    if isinstance(t, str):
+        t = parse(t)
+    elif isinstance(t, np.datetime64):
+        t = t.astype(datetime.datetime)
+    elif isinstance(t, datetime.datetime):
+        pass
+    elif isinstance(t, datetime.date):
+        return t
+    elif isinstance(t, (np.ndarray, list, tuple)):
+        return np.asarray([forceutc(T) for T in t])
+    else:
+        raise TypeError('datetime only input')
+# %% enforce UTC on datetime
+    if t.tzinfo is None:  # datetime-naive
+        t = t.replace(tzinfo=UTC)
+    else:  # datetime-aware
+        t = t.astimezone(UTC)  # changes timezone, preserving absolute time. E.g. noon EST = 5PM UTC
+
+    return t
diff --git a/setup.cfg b/setup.cfg
index 774f0ff..a754917 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,7 +1,8 @@
 [metadata]
 name = sciencedates
-version = 1.4.3
+version = 1.4.4
 author = Michael Hirsch, Ph.D.
+author_email = scivision@users.noreply.github.com
 url = https://github.com/scivision/sciencedates
 description = Date conversions used in the sciences.
 keywords =
@@ -11,17 +12,19 @@ classifiers =
   Development Status :: 5 - Production/Stable
   Environment :: Console
   Intended Audience :: Science/Research
-  License :: OSI Approved :: MIT License
   Operating System :: OS Independent
+  Programming Language :: Python :: 3.5
   Programming Language :: Python :: 3.6
   Programming Language :: Python :: 3.7
+  Programming Language :: Python :: Implementation :: CPython
+  Programming Language :: Python :: Implementation :: PyPy
   Topic :: Utilities
 license_file = LICENSE
 long_description = file: README.md
 long_description_content_type = text/markdown
 
 [options]
-python_requires = >= 3.6
+python_requires = >= 3.5
 setup_requires =
   setuptools >= 38.6
   pip >= 10
@@ -30,19 +33,21 @@ include_package_data = True
 packages = find:
 install_requires =
   numpy
-  pytz
   python-dateutil
 
 [options.extras_require]
 tests =
   pytest
+cov =
   pytest-cov
   coveralls
   flake8
   mypy
-plot = 
-  xarray 
+plot =
+  xarray
   matplotlib
+timezone =
+  pytz
 
 [options.entry_points]
 console_scripts =
@@ -59,7 +64,6 @@ omit =
   /home/travis/virtualenv/*
   */site-packages/*
   */bin/*
-  */build/*
 
 [coverage:report]
 exclude_lines =
diff --git a/tests/test_conv.py b/tests/test_conv.py
index 18254ba..9df7469 100755
--- a/tests/test_conv.py
+++ b/tests/test_conv.py
@@ -2,10 +2,10 @@
 import datetime
 from dateutil.parser import parse
 import numpy as np
-from pytz import timezone
 from numpy.testing import assert_allclose, assert_equal
 import pytest
 import sciencedates as sd
+import sys
 #
 T = [datetime.datetime(2013, 7, 2, 12, 0, 0)]
 T.append(T[0].date())
@@ -13,6 +13,7 @@
 T.append(str(T[0]))
 
 Tdt = (T[0],)*3
+OLDPY = sys.version_info < (3, 6)
 
 
 def test_yearint():
@@ -62,8 +63,11 @@ def test_yeardec():
     assert_equal(sd.yeardec2datetime(sd.datetime2yeardec(Tdt)), T[0])
 
 
+@pytest.mark.xfail(OLDPY, reason='py36+')
 def test_utc():
-    estdt = T[0].astimezone(timezone('EST'))
+    pytz = pytest.importorskip('pytz')
+
+    estdt = T[0].astimezone(pytz.timezone('EST'))
     utcdt = sd.forceutc(estdt)
 
     assert utcdt == estdt
@@ -73,5 +77,8 @@ def test_utc():
     assert sd.forceutc(d) == d
 
 
+if __name__ == '__main__':
+    pytest.main([__file__])
+
 if __name__ == '__main__':
     pytest.main()
diff --git a/tests/test_msis.py b/tests/test_msis.py
index 6bcdf90..ec62e4f 100644
--- a/tests/test_msis.py
+++ b/tests/test_msis.py
@@ -82,4 +82,4 @@ def test_glon():
 
 
 if __name__ == '__main__':
-    pytest.main()
+    pytest.main([__file__])
diff --git a/tests/test_time.py b/tests/test_time.py
index 22b8042..072fd34 100644
--- a/tests/test_time.py
+++ b/tests/test_time.py
@@ -23,4 +23,4 @@ def test_randomdate():
 
 
 if __name__ == '__main__':
-    pytest.main()
+    pytest.main([__file__])