Understanding the importance of testing

Through the years that I have been working in Salesforce, I have too often encountered the following scenarios:

1. Developer receives problem
2. Developer writes code
3. Developer tests through the user interface (UI)
4. They then declare the work as finished and hand it over to the testing team or customer for review
5. Developer writes test methods to achieve 75% code coverage
6. And then, developer deploys the code

The fact that the developer has declared the work as finished before the testing is complete is incorrect and should be discouraged as a practice. As a general rule, code without tests is not finished. A more correct order here would be the following:

1. Developer receives problem
2. Developer writes code
3. Developer writes test methods to achieve at least 95% code coverage
4. Developer tests through the UI
5. They then declare the work as finished and hand it over to the testing team or customer for review...