"RuntimeError: Make sure the Graphviz executables are on your system's path" after installing Graphviz 2.38

I downloaded Graphviz 2.38 MSI version and installed under folder C:\Python34, then I run pip install Graphviz, everything went well. In system's path I added C:\Python34\bin. When I tried to run a test script, in line filename=dot.render(filename='test'), I got a message

 RuntimeError: failed to execute ['dot', '-Tpdf', '-O', 'test'], make sure the Graphviz executables are on your systems' path

I tried to put "C:\Python34\bin\dot.exe" in system's path, but it didn't work, and I even created a new environment variable "GRAPHVIZ_DOT" with value "C:\Python34\bin\dot.exe", still not working. I tried to uninstall Graphviz and pip uninstall graphviz, then reinstall it and pip install again, but nothing works.

The whole traceback message is:

Traceback (most recent call last):  File "C:\Python34\lib\site-packages\graphviz\files.py", line 220, in render    proc = subprocess.Popen(cmd, startupinfo=STARTUPINFO)  File "C:\Python34\lib\subprocess.py", line 859, in __init__    restore_signals, start_new_session)  File "C:\Python34\lib\subprocess.py", line 1112, in _execute_child    startupinfo)FileNotFoundError: [WinError 2] The system cannot find the file specifiedDuring handling of the above exception, another exception occurred:Traceback (most recent call last):  File "C:\Users\Documents\Kissmetrics\curves and lines\eventNodes.py", line 56, in <module>    filename=dot.render(filename='test')  File "C:\Python34\lib\site-packages\graphviz\files.py", line 225, in render'are on your systems\' path' % cmd)RuntimeError: failed to execute ['dot', '-Tpdf', '-O', 'test'], make sure the Graphviz executables are on your systems' path

Does anybody have any experience with it?