doc: convert remaining bash tests to Go

Updates #28387
Updates #30316
Fixes #35574

Change-Id: I21c9e18573909e092ed8dcec91b8542bb97e9f5a
Reviewed-on: https://go-review.googlesource.com/c/go/+/207263
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/codewalk/codewalk_test.go

@@ -0,0 +1,52 @@
+// Copyright 2019 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_test
+
+import (
+	"bytes"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+// TestMarkov tests the code dependency of markov.xml.
+func TestMarkov(t *testing.T) {
+	cmd := exec.Command("go", "run", "markov.go")
+	cmd.Stdin = strings.NewReader("foo")
+	cmd.Stderr = bytes.NewBuffer(nil)
+	out, err := cmd.Output()
+	if err != nil {
+		t.Fatalf("%s: %v\n%s", strings.Join(cmd.Args, " "), err, cmd.Stderr)
+	}
+
+	if !bytes.Equal(out, []byte("foo\n")) {
+		t.Fatalf(`%s with input "foo" did not output "foo":\n%s`, strings.Join(cmd.Args, " "), out)
+	}
+}
+
+// TestPig tests the code dependency of functions.xml.
+func TestPig(t *testing.T) {
+	cmd := exec.Command("go", "run", "pig.go")
+	cmd.Stderr = bytes.NewBuffer(nil)
+	out, err := cmd.Output()
+	if err != nil {
+		t.Fatalf("%s: %v\n%s", strings.Join(cmd.Args, " "), err, cmd.Stderr)
+	}
+
+	const want = "Wins, losses staying at k = 100: 210/990 (21.2%), 780/990 (78.8%)\n"
+	if !bytes.Contains(out, []byte(want)) {
+		t.Fatalf(`%s: unexpected output\ngot:\n%s\nwant output containing:\n%s`, strings.Join(cmd.Args, " "), out, want)
+	}
+}
+
+// TestURLPoll tests the code dependency of sharemem.xml.
+func TestURLPoll(t *testing.T) {
+	cmd := exec.Command("go", "build", "-o", os.DevNull, "urlpoll.go")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("%s: %v\n%s", strings.Join(cmd.Args, " "), err, out)
+	}
+}