Best Practices for Writing Test Class in Salesforce

Apart from the rule that we all are aware of having atleast 75% code coverage , here are the list of best practices which should be followed while writing a Test Class in Salesforce.

Prepare Test Data:
- Instead of relying on the organizations data create your own test Data.
- Create all test data before calling the Test.startTest method.
- Test Data Deletion is not required as test classes uses test data for simulations and dont commit them.
Create separate test classes for all classes and triggers. Never test your entire application in a single test.

Make sure your test covers all the branches of conditional Statements.
Make calls to methods using both valid and invalid inputs.This is often referred as positive and Negative Test..
Always handle all exceptions that are caught, instead of merely catching the exceptions.
Use System.assert methods to check the output is as per the our assumptions.
Use the runAs method to test your application in different user contexts.
Exercise bulk trigger functionality—use at least 100 records in your tests.
Use the ORDER BY keywords to ensure that the records are returned in the expected order.