gocovmerge takes the results from multiple go test -coverprofile runs and merges them into one profile.

gocovmerge [coverprofiles...]

gocovmerge takes the source coverprofiles as the arguments (output from go test -coverprofile coverage.out) and outputs a merged version of the files to standard out. You can only merge profiles that were generated from the same source code. If there are source lines that overlap or do not merge, the process will exit with an error code.