Build tags still apply to test files, so you can do this:
This is file1_test.go:
// +build !Disable1
package test
import "testing"
func Test1(t *testing.T) {}
This is file2_test.go
// +build !Disable2
package test
import "testing"
func Test2(t *testing.T) {}
then you can do this (assume pkg is the import path of the above test package)
go test pkg # run all tests
go test -tags Disable1 pkg # only run Test2
go test -tags Disable2 pkg # only run Test1
go test -tags "Disable1 Disable2" pkg # go tool will show error because you excluded every test file