unit testing

（1） Definition ：

unit testing （ Also known as module testing ） It's for program modules ( The smallest unit of software design ) To test the correctness .

A program unit is the smallest testable part of an application . In procedural programming , A unit is a single program 、 function 、 Process, etc ; For object-oriented programming , The smallest unit is the method , Including base classes （ Superclass ）、 abstract class 、 Or derived classes （ Subclass ） The method in .　  

（2） Unit test tasks include ：

1 Module interface test ;

2 Module local data structure test ;

3 Module boundary condition test ;

4 All in the module independently perform path testing ;

5 Test each error handling path of the module .　　

Module interface testing is the foundation of unit testing . Only if the data can flow in correctly 、 Under the premise of outflow module , Other tests make sense .

The following factors should be considered to test whether the interface is correct ：

1 Whether the number of input actual parameters is the same as that of formal parameters ;　　

2 Whether the input actual parameters match the properties of the formal parameters ;　　

3 Whether the dimensions of the input actual parameters and formal parameters are consistent ;　　

4 Whether the number of actual parameters given when calling other modules is the same as the number of formal parameters of the called module ;　　

5 Whether the attributes of the actual parameters given when calling other modules match the formal parameter attributes of the called module ;　　

6 Whether the dimension of the actual parameters given when calling other modules is consistent with the shape parameter dimension of the module being called ;　　

7 The number of arguments used to call a predefined function 、 Whether the attributes and order are correct ;　　

8 Whether there is a parameter reference independent of the current entry point ;　　

9 Whether the read-only parameter has been modified ;　　

10 Whether the definition of the whole process variable is consistent with each module ;　　

11 Whether to pass some constraints as parameters .　

If external inputs and outputs are included in the module , The following factors should also be considered ：　　

1 Whether the file properties are correct ;　　

2 OPEN/CLOSE Is the statement correct ;　　

3 Whether the format description matches the input / output statement ;　　

4 Whether the buffer size matches the record length ;　　

5 Whether the file has been opened before use ;　　

6 Whether the end of the file has been processed ;　　

7 Is the input processed / Output error ;　　

8 Whether there is any literal error in the output information ;　

　

Checking the local data structure is to ensure that the data temporarily stored in the module is complete during the execution of the program 、 correct .

Local data structures are often the root cause of errors , Test cases should be carefully designed , Try to find the following types of errors ：

1 Description of inappropriate or incompatible types ;　　

2 Variable has no initial value ;　　

3 Error in variable initialization or missing value ;　　

4 Incorrect variable name （ Misspelled or incorrectly truncated ）; 　　

5 Overflow 、 Underflow and address exceptions .　　

In addition to local data structures , If possible , You should also check the global data during unit testing （ for example FORTRAN Public area of ） Impact on modules .　　

Each independent execution path shall be tested in the module , The basic task of unit testing is to ensure that each statement in the module is executed at least once . At this time, the test case is designed to find out that the calculation is wrong 、 Errors caused by incorrect comparison and improper control flow . At this time, basic path testing and loop testing are the most commonly used and effective testing techniques .

Common errors in calculations include ：

　　

1 Misunderstood or misused operator priority ;　　

2 Mixed type operation ;　　

3 The initial value of the variable is wrong ;　　

4 Insufficient precision ;　　

5 The expression symbol is wrong .　

Comparative judgment and control flow are often closely related ,

The test case should also focus on finding the following errors ： 　　

1 Compare objects of different data types ;　　

2 Incorrect use of logical operators or priorities ;　　

3 Due to the limitations of computer representation , Two quantities that are theoretically equal but actually unequal are expected to be equal ;　　

4 Error in comparison operation or variable ;　　

5 Loop termination conditions may or may not occur ;　　

6 You cannot exit while iterating ;　　

7 Incorrectly modified the loop variable .　　

A good design should be able to foresee all kinds of error conditions , And preset various error handling channels , The error handling path also needs to be carefully tested ,

The test should focus on the following problems ：　　

1 The output error message is difficult to understand ;　　

2 The recorded error does not match the error actually encountered ;　　

3 Before the error handling segment customized by the program runs , The system has intervened ;　　

4 Improper exception handling ;　　

5 The Error statement did not provide enough location error information .　　

Boundary condition test is the last of unit test , It is also the most important task . Everyone knows , Software often fails at the boundary , Using boundary value analysis technology , For boundary values and their left 、 Right design test case , It is possible to find new mistakes .   

（3） Unit test process

It is generally believed that unit testing should be immediately after coding , When the source program is compiled and passes the review and compilation check , You can start unit testing . The design of test cases should be combined with the review , Select test data according to design information , It will increase the possibility of discovering the above errors . While determining test cases , The desired results should be given .　　

A driver module should be developed for the test module （driver） and （ or ） Several pile modules （stub）, The following figure shows the general unit test environment . The drive modules are collectively referred to as... In most fields “ The main program ”, It receives test data and passes it to the module under test , After the tested module is called ,“ The main program ” Print “ Get into - sign out ” news .　　

The drive module and pile module are the software used in the test , Not part of a software product , But it requires a certain development cost . If the drive and pile modules are relatively simple , The actual cost is relatively low . However, only using simple driver module and pile module can not complete the test task of some modules , The unit test of these modules can only adopt the comprehensive test method discussed below .　　

Improving the cohesion of modules can simplify unit testing , If each module can only complete one , The number of test cases required will be significantly reduced , Errors in the module are easy to find .