testscript: add ReadFile method (#82)

This allows custom commands to operate on the output of previous
exec commands similar to the built in cp and cmp commands.

Author: rogpeppe

testscript/cmd.go

@@ -119,21 +119,11 @@ func (ts *TestScript) cmdCmpenv(neg bool, args []string) {
 
 func (ts *TestScript) doCmdCmp(args []string, env bool) {
 	name1, name2 := args[0], args[1]
-	var text1, text2 string
-	if name1 == "stdout" {
-		text1 = ts.stdout
-	} else if name1 == "stderr" {
-		text1 = ts.stderr
-	} else {
-		data, err := ioutil.ReadFile(ts.MkAbs(name1))
-		ts.Check(err)
-		text1 = string(data)
-	}
+	text1 := ts.ReadFile(name1)
 
 	data, err := ioutil.ReadFile(ts.MkAbs(name2))
 	ts.Check(err)
-	text2 = string(data)
-
+	text2 := string(data)
 	if env {
 		text2 = ts.expand(text2)
 	}

testscript/testdata/readfile.txt

@@ -0,0 +1,10 @@
+echo stdout stdout
+testreadfile stdout
+
+echo stderr stderr
+testreadfile stderr
+
+testreadfile x/somefile
+
+-- x/somefile --
+x/somefile

testscript/testscript.go

@@ -631,6 +631,27 @@ func (ts *TestScript) MkAbs(file string) string {
 	return filepath.Join(ts.cd, file)
 }
 
+// ReadFile returns the contents of the file with the
+// given name, intepreted relative to the test script's
+// current directory. It interprets "stdout" and "stderr" to
+// mean the standard output or standard error from
+// the most recent exec or wait command respectively.
+//
+// If the file cannot be read, the script fails.
+func (ts *TestScript) ReadFile(file string) string {
+	switch file {
+	case "stdout":
+		return ts.stdout
+	case "stderr":
+		return ts.stderr
+	default:
+		file = ts.MkAbs(file)
+		data, err := ioutil.ReadFile(file)
+		ts.Check(err)
+		return string(data)
+	}
+}
+
 // Setenv sets the value of the environment variable named by the key.
 func (ts *TestScript) Setenv(key, value string) {
 	ts.env = append(ts.env, key+"="+value)

testscript/testscript_test.go

@@ -14,6 +14,7 @@ import (
 	"reflect"
 	"regexp"
 	"strconv"
+	"strings"
 	"testing"
 	"time"
 )
@@ -23,6 +24,17 @@ func printArgs() int {
 	return 0
 }
 
+func echo() int {
+	s := strings.Join(os.Args[2:], " ")
+	switch os.Args[1] {
+	case "stdout":
+		fmt.Println(s)
+	case "stderr":
+		fmt.Fprintln(os.Stderr, s)
+	}
+	return 0
+}
+
 func exitWithStatus() int {
 	n, _ := strconv.Atoi(os.Args[1])
 	return n
@@ -46,6 +58,7 @@ func signalCatcher() int {
 func TestMain(m *testing.M) {
 	os.Exit(RunMain(m, map[string]func() int{
 		"printargs":     printArgs,
+		"echo":          echo,
 		"status":        exitWithStatus,
 		"signalcatcher": signalCatcher,
 	}))
@@ -100,6 +113,16 @@ func TestScripts(t *testing.T) {
 					ts.Fatalf("test-values did not see expected value")
 				}
 			},
+			"testreadfile": func(ts *TestScript, neg bool, args []string) {
+				if len(args) != 1 {
+					ts.Fatalf("testreadfile <filename>")
+				}
+				got := ts.ReadFile(args[0])
+				want := args[0] + "\n"
+				if got != want {
+					ts.Fatalf("reading %q; got %q want %q", args[0], got, want)
+				}
+			},
 		},
 		Setup: func(env *Env) error {
 			infos, err := ioutil.ReadDir(env.WorkDir)