Integration testing approach - Java /Angular

Our project has front end(Angular 6) invoking REST calls to backend(Java SpringBoot).

Database layer has two java subcomponents + liquibase component(for creating MySQL database schema).

Basically a 3-tier web application.

Currently unit testing is done for every layer.

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Coming from C/C++ background, unit & Integration test cases are sitting in subfolders of a project folder(functional code). Integration testing requires overall product knowledge and its domain knowledge.

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1) What is the integration testing approach for 3-tier web application? Written in Spring Boot and Angular..

2) Are their some testing frameworks for integration testing of such applications?