PICs bring photonics into the realm of integrated electronics by merging, in a compact design photonic components such as lasers and modulators with opto-electronic, electro-optical, fully electronic, or even RF functionalities and endless potential in applications. When it comes to optical characterization of PICs, several test solutions and measurement methods exist. This white paper covers the basic principles of optical testing directly on wafers and the best measurement methods for both active and passive components present on the PIC chip.