In black box testing, the tester has zero knowledge of the IT infrastructure. Here, the testers will be unaware of the application, and they would have to gather information all by themselves. Based on the gathered information, testers will identify system vulnerabilities, if any. It is important as it emulates the attack of an external hacker.
A white box attack emulates an insider who can be an employee in the organization trying to make unvalidated profits. In this form of testing, the tester has complete knowledge of the IT infrastructure.