cmd/go: add simple test for generate's line parser

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/128710043

src/cmd/go/generate_test.go

+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"reflect"
+	"runtime"
+	"testing"
+)
+
+type splitTest struct {
+	in  string
+	out []string
+}
+
+var splitTests = []splitTest{
+	{"", nil},
+	{"x", []string{"x"}},
+	{" a b\tc ", []string{"a", "b", "c"}},
+	{` " a " `, []string{" a "}},
+	{"$GOFILE", []string{"proc.go"}},
+	{"a $XXNOTDEFINEDXX b", []string{"a", "", "b"}},
+	{"/$XXNOTDEFINED/", []string{"//"}},
+	{"$GOARCH", []string{runtime.GOARCH}},
+	{"yacc -o $GOARCH/yacc_$GOFILE", []string{"go", "tool", "yacc", "-o", runtime.GOARCH + "/yacc_proc.go"}},
+}
+
+func TestGenerateCommandParse(t *testing.T) {
+	g := &Generator{
+		r:        nil, // Unused here.
+		path:     "/usr/ken/sys/proc.go",
+		dir:      "/usr/ken/sys",
+		file:     "proc.go",
+		pkg:      "sys",
+		commands: make(map[string][]string),
+	}
+	g.setShorthand([]string{"-command", "yacc", "go", "tool", "yacc"})
+	for _, test := range splitTests {
+		got := g.split("//go:generate " + test.in)
+		if !reflect.DeepEqual(got, test.out) {
+			t.Errorf("split(%q): got %q expected %q", test.in, got, test.out)
+		}
+	}
+}