Testing methodologies: –
There are 3-types of testing methodologies are available in testing. 

1) White box Testing

2) Black-box Testing

3) Grey box Testing 

1) White box Testing:-

If one resource is performing testing on the Structural Part (Source code) then it comes under White Box testing.

Developers are the white box testers.

White box testing is an application considering method used to examine the internal structure coding, configuration, design, layout, and inner-working of software application. Developers use this testing method to verify the flow of inputs and outputs through the application, improving usability and design and maintaining security. 

2) Black box Testing:-

If one resource is performing testing on the specific Functional Part or Features of the application under test, then it comes under the Black Box Testing. Does functional Testing mean checking whether the application is developed based on the client’s requirement or not?

Example : 
Checking that it is possible to log in using correct user credentials, and not possible to log in using wrong credentials.

Test Engineers are the Black Box Testers.

3) Grey box Testing:-

If one resource has both black box testing experience and white box testing experience then he became grey box testing.