Why is documentation necessary in QA? What steps are needed to develop and run software tests?

Documentation is very necessary in quality assurance. Everything should be documented. User manuals, test plans, bug reports, business reports, code changes, specifications, design and all other reports should be documented. Any changes in the process should be documented.
A properly documented requirement specification is very necessary. Requirements are the details of what is to be done. Requirements should be clear, complete, detailed, testable. Details should be determined and organized in an efficient way but it can be difficult to handle. Some type of documentation with detailed requirements is very important to properly plan and execute tests.

There are some steps that are needed to develop and run software tests:
- The requirements, design specifications are necessary.
- Budget and cost should be known.
- What people will be responsible, responsibilities, standards and processes should be listed.
- Risk aspects should be determined.
- Test approaches should be defined.
- Test environment should be defined.
- Tasks should be identified.
- Inputs should be determined.
- Test plan document should be prepared.
- Test cases should be written.
- Test environment and test ware should be prepared.
- Tests are performed and results are evaluated.
- Problems are tracked, re-testing is done and test plans are maintained and updated.