pkg/bisect: add initial testing support for cause bisection

(note: incomplete change)

Refactor existing code as follows:
* Move reusable test utility functions from git_repo_test.go to
pkg/vcs/test_util.go and make them exported.
* Split Run() into Run()+runImpl().
* Change type of bisect.go:env.inst to `instance.BuilderTester`.
Change usage inside syz-testbuild/testbuild.go accordingly.
* Move most of linux.PreviousReleaseTags() into vcs/git.go as
git.previousReleaseTags().
* Allow build.CompilerIdentity to be mocked.

Introduce the following changes:
* instance.BuilderTester is an interface with methods
	BuildSyzkaller()
	BuildKernel()
	Test()
NewEnv() now returns this interface.
* type testEnv implements instance.BuilderTester.
* type testBuilder implements builder interface. Add a entry into table
inside pkg/build/build.go:getBuilder() to return testBuilder object.

6 files changed, 186 insertions, 126 deletions

diff --git a/pkg/vcs/git.go b/pkg/vcs/git.go
index 7b0a621b6..359c3d68e 100644
--- a/pkg/vcs/git.go
+++ b/pkg/vcs/git.go
@@ -450,3 +450,27 @@ func (git *git) bisectInconclusive(output []byte) ([]*Commit, error) {
 	}
 	return commits, nil
 }
+
+func (git *git) previousReleaseTags(commit string, self bool) ([]string, error) {
+	var tags []string
+	if self {
+		output, err := git.git("tag", "--list", "--points-at", commit, "--merged", commit, "v*.*")
+		if err != nil {
+			return nil, err
+		}
+		tags, err = gitParseReleaseTags(output)
+		if err != nil {
+			return nil, err
+		}
+	}
+	output, err := git.git("tag", "--no-contains", commit, "--merged", commit, "v*.*")
+	if err != nil {
+		return nil, err
+	}
+	tags1, err := gitParseReleaseTags(output)
+	if err != nil {
+		return nil, err
+	}
+	tags = append(tags, tags1...)
+	return tags, nil
+}
diff --git a/pkg/vcs/git_repo_test.go b/pkg/vcs/git_repo_test.go
index 017aaa658..227834b71 100644
--- a/pkg/vcs/git_repo_test.go
+++ b/pkg/vcs/git_repo_test.go
@@ -10,10 +10,8 @@ import (
 	"path/filepath"
 	"sort"
 	"testing"
-	"time"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/google/syzkaller/pkg/osutil"
 )
 
 func init() {
@@ -21,12 +19,6 @@ func init() {
 	os.Setenv("SYZ_DISABLE_SANDBOXING", "yes")
 }
 
-const (
-	userEmail           = `test@syzkaller.com`
-	userName            = `Test Syzkaller`
-	extractFixTagsEmail = `"syzbot" <syzbot@my.mail.com>`
-)
-
 func TestGitRepo(t *testing.T) {
 	t.Parallel()
 	baseDir, err := ioutil.TempDir("", "syz-git-test")
@@ -34,30 +26,30 @@ func TestGitRepo(t *testing.T) {
 		t.Fatal(err)
 	}
 	defer os.RemoveAll(baseDir)
-	repo1 := createTestRepo(t, baseDir, "repo1")
-	repo2 := createTestRepo(t, baseDir, "repo2")
+	repo1 := CreateTestRepo(t, baseDir, "repo1")
+	repo2 := CreateTestRepo(t, baseDir, "repo2")
 	repo := newGit(filepath.Join(baseDir, "repo"), nil)
 	{
-		com, err := repo.Poll(repo1.dir, "master")
+		com, err := repo.Poll(repo1.Dir, "master")
 		if err != nil {
 			t.Fatal(err)
 		}
-		if diff := cmp.Diff(com, repo1.commits["master"]["1"]); diff != "" {
+		if diff := cmp.Diff(com, repo1.Commits["master"]["1"]); diff != "" {
 			t.Fatal(diff)
 		}
 	}
 	{
-		com, err := repo.CheckoutBranch(repo1.dir, "branch1")
+		com, err := repo.CheckoutBranch(repo1.Dir, "branch1")
 		if err != nil {
 			t.Fatal(err)
 		}
-		if diff := cmp.Diff(com, repo1.commits["branch1"]["1"]); diff != "" {
+		if diff := cmp.Diff(com, repo1.Commits["branch1"]["1"]); diff != "" {
 			t.Fatal(diff)
 		}
 	}
 	{
-		want := repo1.commits["branch1"]["0"]
-		com, err := repo.CheckoutCommit(repo1.dir, want.Hash)
+		want := repo1.Commits["branch1"]["0"]
+		com, err := repo.CheckoutCommit(repo1.Dir, want.Hash)
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -66,7 +58,7 @@ func TestGitRepo(t *testing.T) {
 		}
 	}
 	{
-		commits, err := repo.ListRecentCommits(repo1.commits["branch1"]["1"].Hash)
+		commits, err := repo.ListRecentCommits(repo1.Commits["branch1"]["1"].Hash)
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -76,8 +68,8 @@ func TestGitRepo(t *testing.T) {
 		}
 	}
 	{
-		want := repo2.commits["branch1"]["0"]
-		com, err := repo.CheckoutCommit(repo2.dir, want.Hash)
+		want := repo2.Commits["branch1"]["0"]
+		com, err := repo.CheckoutCommit(repo2.Dir, want.Hash)
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -86,8 +78,8 @@ func TestGitRepo(t *testing.T) {
 		}
 	}
 	{
-		want := repo2.commits["branch1"]["1"]
-		com, err := repo.CheckoutCommit(repo2.dir, want.Hash)
+		want := repo2.Commits["branch1"]["1"]
+		com, err := repo.CheckoutCommit(repo2.Dir, want.Hash)
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -96,16 +88,16 @@ func TestGitRepo(t *testing.T) {
 		}
 	}
 	{
-		com, err := repo.CheckoutBranch(repo2.dir, "branch2")
+		com, err := repo.CheckoutBranch(repo2.Dir, "branch2")
 		if err != nil {
 			t.Fatal(err)
 		}
-		if diff := cmp.Diff(com, repo2.commits["branch2"]["1"]); diff != "" {
+		if diff := cmp.Diff(com, repo2.Commits["branch2"]["1"]); diff != "" {
 			t.Fatal(diff)
 		}
 	}
 	{
-		want := repo2.commits["branch2"]["0"]
+		want := repo2.Commits["branch2"]["0"]
 		com, err := repo.SwitchCommit(want.Hash)
 		if err != nil {
 			t.Fatal(err)
@@ -123,9 +115,9 @@ func TestMetadata(t *testing.T) {
 		t.Fatal(err)
 	}
 	defer os.RemoveAll(repoDir)
-	repo := makeTestRepo(t, repoDir)
+	repo := MakeTestRepo(t, repoDir)
 	for i, test := range metadataTests {
-		repo.commitChange(test.description)
+		repo.CommitChange(test.description)
 		com, err := repo.repo.HeadCommit()
 		if err != nil {
 			t.Fatal(err)
@@ -297,10 +289,10 @@ func TestBisect(t *testing.T) {
 		t.Fatal(err)
 	}
 	defer os.RemoveAll(repoDir)
-	repo := makeTestRepo(t, repoDir)
+	repo := MakeTestRepo(t, repoDir)
 	var commits []string
 	for i := 0; i < 5; i++ {
-		repo.commitChange(fmt.Sprintf("commit %v", i))
+		repo.CommitChange(fmt.Sprintf("commit %v", i))
 		com, err := repo.repo.HeadCommit()
 		if err != nil {
 			t.Fatal(err)
@@ -413,80 +405,3 @@ func TestBisect(t *testing.T) {
 		}
 	}
 }
-
-type testWriter testing.T
-
-func (t *testWriter) Write(data []byte) (int, error) {
-	(*testing.T)(t).Log(string(data))
-	return len(data), nil
-}
-
-func createTestRepo(t *testing.T, baseDir, name string) *testRepo {
-	repo := makeTestRepo(t, filepath.Join(baseDir, name))
-	repo.git("checkout", "-b", "master")
-	repo.commitFileChange("master", "0")
-	for _, branch := range []string{"branch1", "branch2"} {
-		repo.git("checkout", "-b", branch, "master")
-		repo.commitFileChange(branch, "0")
-		repo.commitFileChange(branch, "1")
-	}
-	repo.git("checkout", "master")
-	repo.commitFileChange("master", "1")
-	return repo
-}
-
-type testRepo struct {
-	t       *testing.T
-	dir     string
-	name    string
-	commits map[string]map[string]*Commit
-	repo    *git
-}
-
-func makeTestRepo(t *testing.T, dir string) *testRepo {
-	if err := osutil.MkdirAll(dir); err != nil {
-		t.Fatal(err)
-	}
-	ignoreCC := map[string]bool{
-		"stable@vger.kernel.org": true,
-	}
-	repo := &testRepo{
-		t:       t,
-		dir:     dir,
-		name:    filepath.Base(dir),
-		commits: make(map[string]map[string]*Commit),
-		repo:    newGit(dir, ignoreCC),
-	}
-	repo.git("init")
-	repo.git("config", "--add", "user.email", userEmail)
-	repo.git("config", "--add", "user.name", userName)
-	return repo
-}
-
-func (repo *testRepo) git(args ...string) {
-	if _, err := osutil.RunCmd(time.Minute, repo.dir, "git", args...); err != nil {
-		repo.t.Fatal(err)
-	}
-}
-
-func (repo *testRepo) commitFileChange(branch, change string) {
-	id := fmt.Sprintf("%v-%v-%v", repo.name, branch, change)
-	file := filepath.Join(repo.dir, "file")
-	if err := osutil.WriteFile(file, []byte(id)); err != nil {
-		repo.t.Fatal(err)
-	}
-	repo.git("add", file)
-	repo.git("commit", "-m", id)
-	if repo.commits[branch] == nil {
-		repo.commits[branch] = make(map[string]*Commit)
-	}
-	com, err := repo.repo.HeadCommit()
-	if err != nil {
-		repo.t.Fatal(err)
-	}
-	repo.commits[branch][change] = com
-}
-
-func (repo *testRepo) commitChange(description string) {
-	repo.git("commit", "--allow-empty", "-m", description)
-}
diff --git a/pkg/vcs/linux.go b/pkg/vcs/linux.go
index e12682277..aaca97fe7 100644
--- a/pkg/vcs/linux.go
+++ b/pkg/vcs/linux.go
@@ -31,30 +31,10 @@ func newLinux(dir string) *linux {
 }
 
 func (ctx *linux) PreviousReleaseTags(commit string) ([]string, error) {
-	return ctx.previousReleaseTags(commit, false)
-}
-
-func (ctx *linux) previousReleaseTags(commit string, self bool) ([]string, error) {
-	var tags []string
-	if self {
-		output, err := ctx.git.git("tag", "--list", "--points-at", commit, "--merged", commit, "v*.*")
-		if err != nil {
-			return nil, err
-		}
-		tags, err = gitParseReleaseTags(output)
-		if err != nil {
-			return nil, err
-		}
-	}
-	output, err := ctx.git.git("tag", "--no-contains", commit, "--merged", commit, "v*.*")
-	if err != nil {
-		return nil, err
-	}
-	tags1, err := gitParseReleaseTags(output)
+	tags, err := ctx.git.previousReleaseTags(commit, false)
 	if err != nil {
 		return nil, err
 	}
-	tags = append(tags, tags1...)
 	for i, tag := range tags {
 		if tag == "v4.0" {
 			// Initially we tried to stop at 3.8 because:
diff --git a/pkg/vcs/test_util.go b/pkg/vcs/test_util.go
new file mode 100644
index 000000000..55bd7bccd
--- /dev/null
+++ b/pkg/vcs/test_util.go
@@ -0,0 +1,116 @@
+package vcs
+
+import (
+	"fmt"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/google/syzkaller/pkg/osutil"
+)
+
+const (
+	userEmail           = `test@syzkaller.com`
+	userName            = `Test Syzkaller`
+	extractFixTagsEmail = `"syzbot" <syzbot@my.mail.com>`
+)
+
+type testWriter testing.T
+
+func (t *testWriter) Write(data []byte) (int, error) {
+	(*testing.T)(t).Log(string(data))
+	return len(data), nil
+}
+
+type TestRepo struct {
+	t       *testing.T
+	Dir     string
+	name    string
+	Commits map[string]map[string]*Commit
+	repo    *git
+}
+
+func (repo *TestRepo) git(args ...string) {
+	if _, err := osutil.RunCmd(time.Minute, repo.Dir, "git", args...); err != nil {
+		repo.t.Fatal(err)
+	}
+}
+
+func MakeTestRepo(t *testing.T, dir string) *TestRepo {
+	if err := osutil.MkdirAll(dir); err != nil {
+		t.Fatal(err)
+	}
+	ignoreCC := map[string]bool{
+		"stable@vger.kernel.org": true,
+	}
+	repo := &TestRepo{
+		t:       t,
+		Dir:     dir,
+		name:    filepath.Base(dir),
+		Commits: make(map[string]map[string]*Commit),
+		repo:    newGit(dir, ignoreCC),
+	}
+	repo.git("init")
+	repo.git("config", "--add", "user.email", userEmail)
+	repo.git("config", "--add", "user.name", userName)
+	return repo
+}
+
+func (repo *TestRepo) CommitFileChange(branch, change string) {
+	id := fmt.Sprintf("%v-%v-%v", repo.name, branch, change)
+	file := filepath.Join(repo.Dir, "file")
+	if err := osutil.WriteFile(file, []byte(id)); err != nil {
+		repo.t.Fatal(err)
+	}
+	repo.git("add", file)
+	repo.git("commit", "-m", id)
+	if repo.Commits[branch] == nil {
+		repo.Commits[branch] = make(map[string]*Commit)
+	}
+	com, err := repo.repo.HeadCommit()
+	if err != nil {
+		repo.t.Fatal(err)
+	}
+	repo.Commits[branch][change] = com
+}
+
+func (repo *TestRepo) CommitChange(description string) {
+	repo.git("commit", "--allow-empty", "-m", description)
+}
+
+func (repo *TestRepo) SetTag(tag string) {
+	repo.git("tag", tag)
+}
+
+func CreateTestRepo(t *testing.T, baseDir, name string) *TestRepo {
+	repo := MakeTestRepo(t, filepath.Join(baseDir, name))
+	repo.git("checkout", "-b", "master")
+	repo.CommitFileChange("master", "0")
+	for _, branch := range []string{"branch1", "branch2"} {
+		repo.git("checkout", "-b", branch, "master")
+		repo.CommitFileChange(branch, "0")
+		repo.CommitFileChange(branch, "1")
+	}
+	repo.git("checkout", "master")
+	repo.CommitFileChange("master", "1")
+	return repo
+}
+
+func CloneTestRepo(t *testing.T, baseDir string, name string, originRepo *TestRepo) *TestRepo {
+	dir := filepath.Join(baseDir, name)
+	if err := osutil.MkdirAll(dir); err != nil {
+		t.Fatal(err)
+	}
+	ignoreCC := map[string]bool{
+		"stable@vger.kernel.org": true,
+	}
+	repo := &TestRepo{
+		t:       t,
+		Dir:     dir,
+		name:    filepath.Base(dir),
+		Commits: make(map[string]map[string]*Commit),
+		repo:    newGit(dir, ignoreCC),
+	}
+	repo.git("clone", originRepo.Dir, repo.Dir)
+	return repo
+}
diff --git a/pkg/vcs/testos.go b/pkg/vcs/testos.go
new file mode 100644
index 000000000..f30dd0799
--- /dev/null
+++ b/pkg/vcs/testos.go
@@ -0,0 +1,23 @@
+// Copyright 2019 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package vcs
+
+type testos struct {
+	*git
+}
+
+func newTestos(dir string) *testos {
+	return &testos{
+		git: newGit(dir, nil),
+	}
+}
+
+func (ctx *testos) PreviousReleaseTags(commit string) ([]string, error) {
+	return ctx.git.previousReleaseTags(commit, false)
+}
+func (ctx *testos) EnvForCommit(commit string, kernelConfig []byte) (*BisectEnv, error) {
+	return &BisectEnv{
+		Compiler: "test-compiler-dont-use",
+	}, nil
+}
diff --git a/pkg/vcs/vcs.go b/pkg/vcs/vcs.go
index 77b919d4b..28264522f 100644
--- a/pkg/vcs/vcs.go
+++ b/pkg/vcs/vcs.go
@@ -104,6 +104,8 @@ func NewRepo(os, vm, dir string) (Repo, error) {
 		return newNetBSD(vm, dir), nil
 	case "freebsd":
 		return newFreeBSD(vm, dir), nil
+	case "test":
+		return newTestos(dir), nil
 	}
 	return nil, fmt.Errorf("vcs is unsupported for %v", os)
 }