Provided are techniques for digital twin functional and non-functional simulation testing. An indication is received that digital twin functional and non-functional simulation testing is to start for an application being developed, where a first portion of code for the application has been developed and a second portion of the code for the application has not been developed. Application data and an application landscape are retrieved. The digital twin functional and non-functional simulation testing is performed to identify which functional and non-functional requirements are not being met by the first portion of the code. For the functional and non-functional requirements that are not being met, suggestions are provided for at least one of the first portion and the second portion to meet one or more of the functional and non-functional requirements. One or more of the suggestions are implemented.