1. A method comprising: in response to receiving an initial user input that causes a builder computing system to compile a set of source code for an application into a set of compiled targets, compiling the set of course code into the set of compiled targets; injecting, by the builder computing system and into at least one compiled target of the set of compiled targets, bytecode that represents a conditional statement, wherein the bytecode is injected within the at least one compiled target of the set of compiled targets prior to bytecode that represents program logic of a function in the application, wherein the conditional statement indicates whether an updated version of the function is loaded in memory of a test environment; deploying, by the builder computing system, the set of compiled targets to initiate execution of the application in the test environment, wherein a subset of the set of source code is compiled into an initial subset of the set of compiled targets; after modification to at least the subset of the set of source code, receiving, at the builder computing system, a subsequent user input that causes the builder computing system to compile at least the subset of the set of source code into an updated subset of the set of compiled targets; in response to determining that the updated subset differs from the initial subset, deploying, by the builder computing system and to the test environment, the updated subset of the set of compiled targets to update the application without terminating execution of the application in the test environment; and in response to the conditional statement being satisfied, injecting, by the builder computing system and into the at least one compiled target of the set of compiled targets, bytecode that invokes the updated version of the function.