python内部自带了一个单元测试的模块，PyUnit也就是我们说的：unittest. Official Doc上关于PyUnit的介绍:
The Python unit testing framework, sometimes referred to as “PyUnit,” is a Python language version of JUnit, by Kent Beck and Erich Gamma. JUnit is, in turn, a Java version of Kent’s Smalltalk testing framework. Each is the de facto standard unit testing framework for its respective language.
unittest supports test automation, sharing of setup and shutdown code for tests, aggregation of tests into collections, and independence of the tests from the reporting framework. The unittest module provides classes that make it easy to support these qualities for a set of tests.
To achieve this, unittest supports some important concepts:
A test fixture represents the preparation needed to perform one or more tests, and any associate cleanup actions. This may involve, for example, creating temporary or proxy databases, directories, or starting a server process.
A test case is the smallest unit of testing. It checks for a specific response to a particular set of inputs. unittest provides a base class, TestCase, which may be used to create new test cases.
A test suite is a collection of test cases, test suites, or both. It is used to aggregate tests that should be executed together.
A test runner is a component which orchestrates the execution of tests and provides the outcome to the user. The runner may use a graphical interface, a textual interface, or return a special value to indicate the results of executing the tests. 由于是初次使用PyUnit框架写单元测试脚本，我还是用了简单的测试用例(test case),用了之后才发现，诶！不错～ unittest的简单使用，大概分以下几个方面：