Improve names and documentation in test code.

client/driver/executor/test_harness_test.go

@@ -5,6 +5,7 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -15,50 +16,81 @@ import (
 	"github.com/hashicorp/nomad/nomad/structs"
 )
 
+// testBinary is the path to the running test binary
+var testBinary = os.Args[0]
+
 func TestMain(m *testing.M) {
-	switch os.Getenv("TEST_MAIN") {
+	// The tests in this package recursively execute the test binary produced
+	// by go test. The TEST_MAIN environment variable controls the recursive
+	// execution.
+	switch tm := os.Getenv("TEST_MAIN"); tm {
+	case "":
+		os.Exit(m.Run())
 	case "app":
 		appMain()
 	default:
-		os.Exit(m.Run())
+		fmt.Fprintf(os.Stderr, "unexpected value for TEST_MAIN, \"%s\"\n", tm)
+		os.Exit(1)
 	}
 }
 
+// setTestAppEnv sets the environement of cmd for a recursive call into
+// TestMain.
+func setTestAppEnv(cmd *exec.Cmd) {
+	cmd.Env = append(os.Environ(), "TEST_MAIN=app")
+}
+
 func appMain() {
 	if len(os.Args) < 2 {
 		fmt.Fprintln(os.Stderr, "no command provided")
 		os.Exit(1)
 	}
+
 	args := os.Args[1:]
-	shift := func() string {
+
+	// popArg removes the first argument from args and returns it.
+	popArg := func() string {
 		s := args[0]
 		args = args[1:]
 		return s
 	}
+
+	// execute a sequence of operations from args
 	for len(args) > 0 {
-		switch cmd := shift(); cmd {
+		switch cmd := popArg(); cmd {
+
 		case "sleep":
+			// sleep <dur>: sleep for a duration indicated by the first
+			// argument
 			if len(args) < 1 {
 				fmt.Fprintln(os.Stderr, "expected arg for sleep")
 				os.Exit(1)
 			}
-			dur, err := time.ParseDuration(shift())
+			dur, err := time.ParseDuration(popArg())
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "could not parse sleep time: %v", err)
 				os.Exit(1)
 			}
 			time.Sleep(dur)
+
 		case "echo":
+			// echo <msg ...>: write the remaining arguments to stdout each
+			// separated by a single space and followed by a newline.
 			fmt.Println(strings.Join(args, " "))
 			args = args[:0]
+
 		case "write":
+			// write <msg> <file>: write a message to a file. The first
+			// argument is the msg. The second argument is the path to the
+			// target file.
 			if len(args) < 2 {
 				fmt.Fprintln(os.Stderr, "expected two args for write")
 				os.Exit(1)
 			}
-			msg := shift()
-			file := shift()
+			msg := popArg()
+			file := popArg()
 			ioutil.WriteFile(file, []byte(msg), 0666)
+
 		default:
 			fmt.Fprintln(os.Stderr, "unknown command:", cmd)
 			os.Exit(1)
@@ -99,7 +131,7 @@ func testExecutor(t *testing.T, buildExecutor func() Executor, compatible func(*
 	command := func(name string, args ...string) Executor {
 		e := buildExecutor()
 		SetCommand(e, name, args)
-		e.Command().Env = append(os.Environ(), "TEST_MAIN=app")
+		setTestAppEnv(e.Command())
 		return e
 	}
 
@@ -132,7 +164,7 @@ func Executor_Start_Invalid(t *testing.T, command buildExecCommand) {
 }
 
 func Executor_Start_Wait_Failure_Code(t *testing.T, command buildExecCommand) {
-	e := command(os.Args[0], "fail")
+	e := command(testBinary, "fail")
 
 	if err := e.Limit(constraint); err != nil {
 		log.Panicf("Limit() failed: %v", err)
@@ -165,7 +197,7 @@ func Executor_Start_Wait(t *testing.T, command buildExecCommand) {
 	expected := "hello world"
 	file := filepath.Join(allocdir.TaskLocal, "output.txt")
 	absFilePath := filepath.Join(taskDir, file)
-	e := command(os.Args[0], "sleep", "1s", "write", expected, file)
+	e := command(testBinary, "sleep", "1s", "write", expected, file)
 
 	if err := e.Limit(constraint); err != nil {
 		log.Panicf("Limit() failed: %v", err)
@@ -204,7 +236,7 @@ func Executor_Start_Kill(t *testing.T, command buildExecCommand) {
 	}
 
 	filePath := filepath.Join(taskDir, "output")
-	e := command(os.Args[0], "sleep", "1s", "write", "failure", filePath)
+	e := command(testBinary, "sleep", "1s", "write", "failure", filePath)
 
 	if err := e.Limit(constraint); err != nil {
 		log.Panicf("Limit() failed: %v", err)
@@ -242,7 +274,7 @@ func Executor_Open(t *testing.T, command buildExecCommand, newExecutor func() Ex
 	expected := "hello world"
 	file := filepath.Join(allocdir.TaskLocal, "output.txt")
 	absFilePath := filepath.Join(taskDir, file)
-	e := command(os.Args[0], "sleep", "1s", "write", expected, file)
+	e := command(testBinary, "sleep", "1s", "write", expected, file)
 
 	if err := e.Limit(constraint); err != nil {
 		log.Panicf("Limit() failed: %v", err)