Add unit test

Signed-off-by: Xianglin Gao <xlgao@zju.edu.cn>

pkg/os/testing/fake_os.go

@@ -19,6 +19,7 @@ package testing
 import (
 	"io"
 	"os"
+	"sync"
 
 	"golang.org/x/net/context"
 
@@ -29,20 +30,64 @@ import (
 // If a member of the form `*Fn` is set, that function will be called in place
 // of the real call.
 type FakeOS struct {
+	sync.Mutex
 	MkdirAllFn  func(string, os.FileMode) error
 	RemoveAllFn func(string) error
 	OpenFifoFn  func(context.Context, string, int, os.FileMode) (io.ReadWriteCloser, error)
+	StatFn      func(name string) (os.FileInfo, error)
+	errors      map[string]error
 }
 
 var _ osInterface.OS = &FakeOS{}
 
+// getError get error for call
+func (f *FakeOS) getError(op string) error {
+	f.Lock()
+	defer f.Unlock()
+	err, ok := f.errors[op]
+	if ok {
+		delete(f.errors, op)
+		return err
+	}
+	return nil
+}
+
+// InjectError inject error for call
+func (f *FakeOS) InjectError(fn string, err error) {
+	f.Lock()
+	defer f.Unlock()
+	f.errors[fn] = err
+}
+
+// InjectErrors inject errors for calls
+func (f *FakeOS) InjectErrors(errs map[string]error) {
+	f.Lock()
+	defer f.Unlock()
+	for fn, err := range errs {
+		f.errors[fn] = err
+	}
+}
+
+// ClearErrors clear errors for call
+func (f *FakeOS) ClearErrors() {
+	f.Lock()
+	defer f.Unlock()
+	f.errors = make(map[string]error)
+}
+
 // NewFakeOS creates a FakeOS.
 func NewFakeOS() *FakeOS {
-	return &FakeOS{}
+	return &FakeOS{
+		errors: make(map[string]error),
+	}
 }
 
 // MkdirAll is a fake call that invokes MkdirAllFn or just returns nil.
 func (f *FakeOS) MkdirAll(path string, perm os.FileMode) error {
+	if err := f.getError("MkdirAll"); err != nil {
+		return err
+	}
+
 	if f.MkdirAllFn != nil {
 		return f.MkdirAllFn(path, perm)
 	}
@@ -51,6 +96,10 @@ func (f *FakeOS) MkdirAll(path string, perm os.FileMode) error {
 
 // RemoveAll is a fake call that invokes RemoveAllFn or just returns nil.
 func (f *FakeOS) RemoveAll(path string) error {
+	if err := f.getError("RemoveAll"); err != nil {
+		return err
+	}
+
 	if f.RemoveAllFn != nil {
 		return f.RemoveAllFn(path)
 	}
@@ -59,8 +108,24 @@ func (f *FakeOS) RemoveAll(path string) error {
 
 // OpenFifo is a fake call that invokes OpenFifoFn or just returns nil.
 func (f *FakeOS) OpenFifo(ctx context.Context, fn string, flag int, perm os.FileMode) (io.ReadWriteCloser, error) {
+	if err := f.getError("OpenFifo"); err != nil {
+		return nil, err
+	}
+
 	if f.OpenFifoFn != nil {
 		return f.OpenFifoFn(ctx, fn, flag, perm)
 	}
 	return nil, nil
 }
+
+// Stat is a fake call that invokes Stat or just return nil.
+func (f *FakeOS) Stat(name string) (os.FileInfo, error) {
+	if err := f.getError("Stat"); err != nil {
+		return nil, err
+	}
+
+	if f.StatFn != nil {
+		return f.StatFn(name)
+	}
+	return nil, nil
+}