Golang exec command unit test

exec.go

package main

import (
  "fmt"
  "os/exec"
  "strconv"
  "strings"
)

var execCommand = exec.Command

func ls() (string, error) {
  cmd := execCommand("ls")
  out, err := cmd.CombinedOutput()
  if err != nil {
    fmt.Printf(string(out))
    return string(out), err
  }
  return string(out), nil
}

func ssh(p int, in string) (string, error) {
  cmd := execCommand("ssh", "root@localhost", "-p", strconv.Itoa(p))
  cmd.Stdin = strings.NewReader(in)
  out, err := cmd.CombinedOutput()
  if err != nil {
    fmt.Printf(string(out))
    return string(out), err
  }
  return string(out), nil
}

func main() {
  r, _ := ls()
  fmt.Print(r)
  p := 32768
  in := "touch hoge\ntouch piyo\n"
  ssh(p, in)
}

exec_test.go

package main

import (
  "fmt"
  "io/ioutil"
  "os"
  "os/exec"
  "strings"
  "testing"
)

const stub = "test_file\ntest_file2\n"

var testCase string

func fakeExecCommand(command string, args ...string) *exec.Cmd {
  cs := []string{"-test.run=TestHelperProcess", "--", command}
  cs = append(cs, args...)
  cmd := exec.Command(os.Args[0], cs...)
  tc := "TEST_CASE=" + testCase
  cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1", tc}
  return cmd
}

func TestHelperProcess(t *testing.T) {
  if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
    return
  }
  defer os.Exit(0)
  args := os.Args
  for len(args) > 0 {
    if args[0] == "--" {
      args = args[1:]
      break
    }
    args = args[1:]
  }
  if len(args) == 0 {
    fmt.Fprintf(os.Stderr, "No command\n")
    os.Exit(2)
  }
  switch os.Getenv("TEST_CASE") {
  case "case1":
    fmt.Fprint(os.Stdout, stub)
  case "case2":
    e := "ssh root@localhost -p 22"
    if s := strings.Join(args, " "); s != e {
      fmt.Fprintf(os.Stderr, "Error: want %q, got %q", e, s)
      os.Exit(1)
    }
    b, err := ioutil.ReadAll(os.Stdin)
    if err != nil {
      fmt.Fprintf(os.Stderr, "Error: %v\n", err)
      os.Exit(1)
    }
    e = "touch aaa\ntouch bbb\n"
    if s := string(b); s != e {
      fmt.Fprintf(os.Stderr, "Error: Read %q, want %q", s, e)
      os.Exit(1)
    }
  }
}

func TestLs(t *testing.T) {
  testCase = "case1"
  execCommand = fakeExecCommand
  defer func() { execCommand = exec.Command }()
  out, err := ls()
  if err != nil {
    t.Fatal(out)
  }
  if out != stub {
    t.Fatalf("Error: want %q, got %q", stub, out)
  }
}

func TestSsh(t *testing.T) {
  testCase = "case2"
  execCommand = fakeExecCommand
  defer func() { execCommand = exec.Command }()
  out, err := ssh(22, "touch aaa\ntouch bbb\n")
  if err != nil {
    t.Fatal(out)
  }
}

Since the tests run in parallel (https://stackoverflow.com/questions/24375966/does-go-test-run-unit-tests-concurrently , https://github.com/golang/go/blob/182bdbb1e1d62fe53f8386e7b02c7738898d373b/src/testing/testing.go#L555), isn't there concurrent access to var testCase string leading to unexpected behaviors?

You're right. This test code cannot consider parallel run.