1. A computer program product, comprising: A non-transitory computer-readable storage medium having computer readable program code embodied therewith, the computer readable program code configured to perform an operation for managing assertions, the operation comprising: receiving, from a user interacting with an integrated development environment (IDE) tool, a request to add an assertion at a specified location within source code of an application, wherein the source code is stored in a first file associated with a development project and wherein the first file does not include information about the assertion; receiving a definition for the assertion, wherein the definition includes one or more lines of source code, an expiration time, and a number of times to insert the assertion into the source code, when compiling the application from the source code; storing the definition for the assertion in a second file associated with the development project; creating an association in the development project between the source code of the application and the assertion, wherein the association is not stored in the first file and indicates at least a line in the first file at which to insert the assertion prior to compiling the source code; receiving a request to compile the source code of the application; modifying the source code stored in the first file by inserting the one or more lines of source code included in the assertion definition at the specified location in the source code; and compiling the application from the source code in the first file.