Test Driven Development

This is a demonstration and somewhat of a guide on developing in a TDD style. For the moment, this project will only demonstrate the unit test aspect of TDD. Unit tests are invaluable when developing any project, and gives you the confidence you need to make changes as the project grows. It is certainly a difficult habit to get into, but it is definitely worth the effort.

Going through the commits, you will see that most commits come with a corresponding set of test methods. To get a sense of what it's like developing in a TDD style, in the hopes that you too will adopt this style of developing, you should read the describe function, and then the subsequent it function that follow.

The describe function is meant to set the focus of the subsequent unit tests. The it function itself is the extremely specific scenario for which we will test. It is the unit test. The it function will set the focus for what "feature" we are trying to achieve. You could also say that the function is trying to focus on the behavior we wish to see. This is also why this style of development is also sometimes called Behavior Driven Development.

Below is the specification of what we want to achieve. It is definitely an arbitrary project chosen for this TDD guide, and definitely not an assignment from my Operating Systems course that I used as a pawn for this guide.

Create an Operating System

Tasks

Ask user about the system

$ How much memory does your system have? (in bytes, max: 4 Billion)
$ Memory: 2000000000
$
$ How many hard disks does your system have?
$ Disks: 2
$
$ How many printers are connected to this system?
$ Printers: 1

Given:

The system is single-core CPU

Key Inputs

A

New process has arrived

Tip: name the ids incrementally, and do not reuse the id when the program terminates

Ask user for the process size (in bytes)
Ask user for the Process Priority (higher number higher priority)

t

Currently running process on CPU is terminated

p <int>

The currently running process on CPU has requested to use printer

Ask for file name to print.

P <int>

An interrupt from the printer saying that the printing job is finished

d <int>

The currently running process has requested to do some disk operation on disk <int>

Ask for file name to read.

D <int>

An interrupt from the disk number that the disk job is done

Sr

Show the ready-queue and current process on CPU

Si

Show information about all I/O devices

Sm

Show information about memory

Where in memory different processes are located
"Best-fit" Allocation
cannot create an array of 4 Billion

E.g.

Bytes 0-999 Belong to process 1

Bytes 1000-1499 Belong to process 2

Extra info

CPU Scheduling

Preemptive Priority Scheduling

I/O Scheduling

FIFO

Memory Management

"Best Fit"
If no room in memory, refuse the process

Example

$ >> A
$    Size: 1000
$    Priority: 5
$ >>
$ >> A
$    Size: 1600
$    Priority: 7
$ >>
$ >> Sr
$    CPU: pid 2
$    Ready: pid 1
$ >> p1
$    File Name: "asdf.txt"
$ >> Sr
$    CPU: pid 1
$    Ready: none
$ >> Si
$    Printer1: pid 2: "asdf.txt"
$    Disk1: none
$    Disk2: none (can avoid printing anything about empty devices)
$ >> P1
$ >> Sr
$    CPU: pid 2
$    Ready: pid 1
$ >> Si
$ >> A
$    Size: 1000
$    Priority: 6
$ >> Sr
$    CPU: pid 2
$    Ready: pid 3, pid 1
$ >> t
$ >> Sr
$    CPU: pid 3
$    Ready: pid 1
$ >> Sm
$    0-1024: P1
$    1525-2524: P3
$ >> A
$    Size: 400
$    Priority: 2
$ >> Sm
$    0-1024: P1
$    1025-1424: P4
$    1525-2524: P3

IgorGee/OS-TDD