! go test -json

stdout '"Action":"output","Package":"p","Test":"Test","Output":"=== RUN   Test\\n","OutputType":"frame"'
stdout '"Action":"output","Package":"p","Test":"Test","Output":"    x_test.go:6: Error1\\n","OutputType":"error"'
stdout '"Action":"output","Package":"p","Test":"Test","Output":"        Error2\\n","OutputType":"error-continue"'
stdout '"Action":"output","Package":"p","Test":"Test","Output":"--- FAIL: Test \([\d.]+s\)\\n","OutputType":"frame"'

-- go.mod --
module p

-- x_test.go --
package p

import "testing"

func Test(t *testing.T) {
	t.Error("Error1\nError2")
}