go test runs concurrently on package level. If I have 2 packages, package A and package B with tests in them, when you run go test, tests in package A and package B will run concurrently at the same time. It is done to run tests faster and make the feedback process fast. But sometime there is need to run tests in sequential order (to keep shared state etc.).
go build provides a flag to do that, that flag is -p.
-p n
the number of programs, such as build commands or
test binaries, that can be run in parallel.
The default is the number of CPUs available.
When using -p flag with go test, such as go test -p 1 ./... will run tests for one package at a time, the total running time for tests is going to be close to the sum of all individual package tests plus build times.