Testing

Dr Andy Evans & Dr Kirk Harland

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Timing a program

• Get the current time in various places and print it out.
  long time = System.currentTimeMillis()
  Where milliseconds is since January 1, 1970, 00:00:00 GMT.
  
• If you want to see this as a proper date, use a java.util.Date object
  new Date(long milliseconds)
  Methods to find if a date is before or after a Date, or set the date in it.
  

Checking memory

• Computers store most of the information they need to do processing in a memory chip.
• If the space available is exceeded by the data, most write to 'Virtual Memory' - this is part of the harddrive and acts as if it's 'real' memory.
• Using Virtual Memory is slow, because it uses magnetic media that are slow to write to.
• If the Virtual Memory is exceeded, processing will become very slow, and the system unstable.

Finding out
about the computer

• Remember, the environment the program is running in is encapsulated by a java.lang.Runtime object.
• The current Runtime can be got with a static method.
  Runtime rt = Runtime.getRuntime();
• Runtime has methods to
  • Deal with the computer memory.
  • Interact with the JVM interpreter.

Computer memory

• Java copes with memory well, but occasionally we may want to check it.
• For example, if a file is much larger than the real memory, we may want to only read in small chunks at a time.

	
runtimeObject.freeMemory()
runtimeObject.totalMemory()

• These return the free and total memory available in the computer.

Garbage Collection

• 'Garbage Collection' is a general computing term for clearing up objects we no longer need from memory.
• Objects will stay in memory until collected, even if not used.
• Java does automatic Garbage Collection, when memory gets low, but you may want to force it.

	
runtimeObject.gc();

Unit Testing

• A way to ensure that methods have the desired 'behaviour'
  • Decide on behaviour
  • Write tests
  • Write code to satisfy tests
• Time consuming
• Produces robust code
• Future maintenance is easier

Other tests

• Stress testing
• Alpha/Beta releases
• Usability
• Regression testing
• Software testing

Summary

• Good code structure centres on building to interfaces: are the inputs and outputs to methods and classes reliable, and do they respond well if things go wrong.
• Get this right, and you'll minimise bugs.
• Unit testing formalises this.
• However, also test usability and go through alpha and beta test releases.