diff --git a/README.rst b/README.rst
index 26e7919..277fa7e 100644
--- a/README.rst
+++ b/README.rst
@@ -7,7 +7,7 @@ INSTALLATION
 pytictoc can be installed and updated via conda or pip.
 
 **pip** ::
- 
+
   pip install pytictoc
   pip install pytictoc --upgrade
 
@@ -19,7 +19,7 @@ pytictoc can be installed and updated via conda or pip.
 
 =============
 USAGE
-============= 
+=============
 
 Basic usage: ::
 
@@ -35,6 +35,14 @@ A string passed to the toc method changes the printed message. This can be usefu
   >> t.toc('Section 1 took')
   Section 1 took 16.494467 seconds.
 
+The default message can also be passed in the constructor, for easier usage with context managers: ::
+
+  >> with TicToc(default_msg='Section 1 took'):
+  >>     ...
+  Section 1 took 16.494467 seconds.
+
+The string passed to toc will override the string in the constructor if both are present.
+
 An optional keyword argument restarts the timer (equivalent to t.tic()) after reporting the time elapsed. ::
 
   >> t.toc(restart=True)
@@ -48,8 +56,12 @@ If you want to return the time elapsed to a variable rather than printing it, us
   >>spam
   20.156261717544602
 
+You can also pass in an alternative stream to print to: ::
+
+  >> t = TicToc(stream=mystream)
+
 The TicToc class can be used within a context manager as an alternative way to time a section of code. The time taken to run the code inside the with statement will be reported on exit. ::
- 
+
   >>with TicToc():
   >>    spam = [x+1 for x in range(10000)]
   Elapsed time is 0.002343 seconds.
@@ -58,7 +70,7 @@ The TicToc class can be used within a context manager as an alternative way to t
 Determining and setting the timer
 ------------------------------------
 
-pytictoc uses timeit.default_timer to time code. On Python 3.3 and later, this is an alias for time.perf_counter. On earlier versions of Python it is an alias for the most precise timer for a given system. 
+pytictoc uses timeit.default_timer to time code. On Python 3.3 and later, this is an alias for time.perf_counter. On earlier versions of Python it is an alias for the most precise timer for a given system.
 
 To see which function is being used: ::
 
@@ -66,9 +78,14 @@ To see which function is being used: ::
   >>pytictoc.default_timer
   <function time.perf_counter>
 
-You can change the timer by simple assignment. ::
-  
+You can change the timer by simple assignment: ::
+
   >>import time
   >>pytictoc.default_timer = time.clock
   >>pytictoc.default_timer
   <function time.clock>
+
+Or by passing a different timer function into an object's constructor: ::
+
+  >>import time
+  >>pytictoc.TicToc(timer=time.clock)
diff --git a/__init__.py b/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/pytictoc.py b/pytictoc.py
index 031ed8d..c80e0ab 100644
--- a/pytictoc.py
+++ b/pytictoc.py
@@ -10,68 +10,95 @@
 __version__      = '1.5.2'
 __version_date__ = '23 April 2021'
 
-
+import sys
 from timeit import default_timer
 
+
 class TicToc(object):
-    
+
     """
     Replicate the functionality of MATLAB's tic and toc.
-    
+
     #Methods
     TicToc.tic()       #start or re-start the timer
     TicToc.toc()       #print elapsed time since timer start
     TicToc.tocvalue()  #return floating point value of elapsed time since timer start
-    
+
     #Attributes
-    TicToc.start     #Time from timeit.default_timer() when t.tic() was last called
-    TicToc.end       #Time from timeit.default_timer() when t.toc() or t.tocvalue() was last called
+    TicToc.start     #Time from timeit.self.timer() when t.tic() was last called
+    TicToc.end       #Time from timeit.self.timer() when t.toc() or t.tocvalue() was last called
     TicToc.elapsed   #t.end - t.start; i.e., time elapsed from t.start when t.toc() or t.tocvalue() was last called
     """
-    
-    def __init__(self):
-        """Create instance of TicToc class."""
+
+    def __init__(self, default_msg='Elapsed time is', stream=None, timer=None):
+        """
+        Create instance of TicToc class.
+
+        Optional arguments:
+            default_msg     - String to replace default message of 'Elapsed time is'
+            stream          - Stream to write the timer message to
+            timer           - Function that returns the current time when called
+        """
+
         self.start   = float('nan')
         self.end     = float('nan')
         self.elapsed = float('nan')
-        
+        self.default_msg = default_msg
+        self.stream = stream or sys.stdout
+
+        # Lazily accessing default timer allows the user to override it later per the docs.
+        self.timer = timer or (lambda: default_timer())
+        assert self.timer is not None
+        assert self.default_msg is not None
+        assert self.stream is not None
+
     def tic(self):
         """Start the timer."""
-        self.start = default_timer()
-        
-    def toc(self, msg='Elapsed time is', restart=False):
+        self.start = self.timer()
+
+    def toc(self, msg=None, restart=False):
         """
         Report time elapsed since last call to tic().
-        
+
         Optional arguments:
-            msg     - String to replace default message of 'Elapsed time is'
+            msg     - String to replace default message initialized with the object
             restart - Boolean specifying whether to restart the timer
         """
-        self.end     = default_timer()
-        self.elapsed = self.end - self.start
-        print('%s %f seconds.' % (msg, self.elapsed))
-        if restart:
-            self.start = default_timer()
-        
+        if msg is None:
+            msg = self.default_msg
+
+        self.tocvalue(restart=restart)
+        print(self._tocmsg(msg, self.elapsed), file=self.stream)
+
     def tocvalue(self, restart=False):
         """
         Return time elapsed since last call to tic().
-        
+
         Optional argument:
             restart - Boolean specifying whether to restart the timer
         """
-        self.end     = default_timer()
+        self.end     = self.timer()
         self.elapsed = self.end - self.start
         if restart:
-            self.start = default_timer()
+            self.start = self.timer()
         return self.elapsed
-    
+
+    def _tocmsg(self, prefix_msg, elapsed):
+        """
+        Return full message that will be output on toc().
+
+        Arguments:
+            prefix_msg: preamble to the timer output
+            elapsed: time elapsed
+        """
+        return '%s %f seconds.' % (prefix_msg, elapsed)
+
     def __enter__(self):
         """Start the timer when using TicToc in a context manager."""
-        self.start = default_timer()
-    
+        self.start = self.timer()
+
     def __exit__(self, *args):
-        """On exit, pring time elapsed since entering context manager."""
-        self.end = default_timer()
+        """On exit, print time elapsed since entering context manager."""
+        self.end = self.timer()
         self.elapsed = self.end - self.start
-        print('Elapsed time is %f seconds.' % self.elapsed)
+        print(self._tocmsg(self.default_msg, self.elapsed), file=self.stream)
diff --git a/testing/__init__.py b/testing/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/testing/pytictoc_test.py b/testing/pytictoc_test.py
new file mode 100644
index 0000000..9d5f94b
--- /dev/null
+++ b/testing/pytictoc_test.py
@@ -0,0 +1,152 @@
+import contextlib
+import re
+import time
+import unittest
+from abc import ABCMeta
+from io import StringIO
+
+from .. import pytictoc as ptt
+
+
+class BaseTicTocTest(unittest.TestCase, metaclass=ABCMeta):
+
+    def setUp(self):
+        self.mock_time = 0
+        self.stream = StringIO()
+        self.mock_timer = lambda: self.mock_time
+        self.tt = ptt.TicToc(default_msg="Time:", stream=self.stream, timer=self.mock_timer)
+
+    def output(self):
+        return self.stream.getvalue()
+
+    def times_passed(self):
+        return re.findall(r'([-\d\.,]+) seconds.$', self.output(), re.MULTILINE)
+
+    def last_time_passed(self):
+        times_passed = self.times_passed()
+        self.assertGreater(len(times_passed), 0, self.err_msg())
+        return float(times_passed[-1])
+
+    def err_msg(self):
+        raw_output = self.output().splitlines() or ["<null>"]
+        return "Last output: %s" % raw_output[-1]
+
+    def _run_tictoc(self, start_time, end_time, work_function=None, **toc_args):
+        self.mock_time = start_time
+        self.tt.tic()
+        if work_function:
+            work_function()
+        self.mock_time = end_time
+        self.tt.toc(**toc_args)
+
+    def tictoc(self, start_time=0, end_time=0, **toc_args):
+        self._run_tictoc(start_time, end_time, **toc_args)
+        self.assertTime(start_time, self.tt.start)
+        self.assertTime(end_time, self.tt.end)
+        self.assertTime(end_time - start_time, self.last_time_passed())
+        self.assertTime(end_time - start_time, self.tt.tocvalue())
+
+    def assertTime(self, expected, actual, *args, **kwargs):
+        # Measure equality to 6 decimal places to avoid float precision errors
+        self.assertAlmostEqual(expected, actual, 6, self.err_msg(), *args, **kwargs)
+
+    def test_increment(self):
+        self.tictoc(0, 1)
+        self.tictoc(0, 2)
+        self.tictoc(5, 9)
+        self.tictoc(-9, 20)
+
+    def test_no_time_passed(self):
+        self.tictoc(0, 0)
+        self.tictoc(1, 1)
+        self.tictoc(-5, -5)
+
+    def test_decrement(self):
+        self.tictoc(1, 0)
+        self.tictoc(5, -5)
+        self.tictoc(-100, -300)
+
+    def test_decimal(self):
+        self.tictoc(0.3, 3.6)
+        self.tictoc(0.3, -3.6)
+        self.tictoc(0.34, 0)
+        self.tictoc(0, -0.25)
+        self.tictoc(-7.9, -20)
+        self.tictoc(4, 25.89)
+
+    def test_default_msg(self):
+        self.tt = ptt.TicToc(stream=self.stream, timer=self.mock_timer)
+        self.tictoc(4, 6)
+        self.assertIn("Elapsed time is 2.0", self.output())
+
+    def test_default_stream_is_stdout(self):
+        with contextlib.redirect_stdout(self.stream):
+            self.tt = ptt.TicToc(default_msg="Time:", timer=self.mock_timer)
+            self.tictoc(-4, 8.2)
+            self.tictoc(8, 16)
+
+    def test_default_invocation_works(self):
+        with contextlib.redirect_stdout(self.stream):
+            self.tt = ptt.TicToc()
+
+            # I suggest keeping a negative interval to confirm the actual time is used
+            self._run_tictoc(0, -1, lambda: time.sleep(0.01))
+
+            # NB: Prior to Python 3.5 the sleep could end early. Will still work with zero.
+            self.assertGreaterEqual(self.last_time_passed(), 0)
+
+    def test_setting_default_timer(self):
+        self.tt = ptt.TicToc(stream=self.stream)
+        old_timer = ptt.default_timer
+        try:
+            ptt.default_timer = self.mock_timer
+            self.tictoc(4, 60)
+            self.tictoc(5, -2)
+        finally:
+            ptt.default_timer = old_timer
+
+    def test_not_setting_default_timer(self):
+        self.tt = ptt.TicToc(stream=self.stream)
+        self._run_tictoc(5, -2)
+        self.assertGreaterEqual(self.last_time_passed(), 0)
+
+
+class TicTocTest(BaseTicTocTest):
+    def test_msg(self):
+        self.tictoc(1, 6, msg="Tic Toc")
+        self.assertIn("Tic Toc 5.0", self.output())
+
+    def test_msg_in_stdout(self):
+        with contextlib.redirect_stdout(self.stream):
+            self.tt = ptt.TicToc(default_msg="Time:", timer=self.mock_timer)
+            self.tictoc(1, -7, msg="Tic Toc")
+            self.assertIn("Tic Toc -8.0", self.output())
+            self.assertNotIn("Time:", self.output())
+
+    def test_restart(self):
+        self._run_tictoc(4, 6, restart=True)
+        self.assertTime(6, self.tt.start)
+
+
+class TicTocTestWithContextManager(BaseTicTocTest):
+    def _run_tictoc(self, start_time, end_time, **toc_args):
+        if toc_args:
+            raise unittest.SkipTest("Toc arguments aren't supported with context managers")
+
+        self.mock_time = start_time
+        with self.tt:
+            self.mock_time = end_time
+
+    def test_default_invocation_works(self):
+        with contextlib.redirect_stdout(self.stream):
+            self.tt = ptt.TicToc()
+            with self.tt:
+                time.sleep(0.01)
+            # NB: Prior to Python 3.5 the sleep could end early. Will still work with zero.
+            self.assertGreaterEqual(self.last_time_passed(), 0)
+
+
+del BaseTicTocTest  # Don't run the tests in the abstract class.
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/testing/test_pytictoc.py b/testing/test_pytictoc.py
index 0e0798b..36b1049 100644
--- a/testing/test_pytictoc.py
+++ b/testing/test_pytictoc.py
@@ -8,45 +8,48 @@
 
 if sys.version_info.major == 3:
     from importlib import reload
-    
-os.chdir(r'C:\Users\ecfne\Documents\Eric\Coding\Python\pytictoc')
+
+os.chdir(os.path.dirname(os.getcwd()))
 
 try:
     reload(pytictoc)
 except (NameError, ImportError):
     import pytictoc
-    
+
+
 def waste_time(num_reps=1000000):
     for i in range(num_reps):
         spam = i+1
         eggs = spam**2
         pancakes = eggs % 3
-    
+
+
 def main():
 
     print('\npytictoc file:')
     print(pytictoc.__file__ + '\n')
-    
+
     t = pytictoc.TicToc()
-    
+
     t.tic()
     waste_time()
     t.toc()
-    
+
     with pytictoc.TicToc():
         waste_time()
-    
+
     t.toc('It has been', restart=True)
     t.toc()
-    
+
     spam = t.tocvalue()
     print(spam)
-    
+
     waste_time()
-    
+
     spam = t.tocvalue(restart=True)
     print(spam)
     t.toc()
-    
+
+
 if __name__ == '__main__':
     main()