Improves Test Coverage by covering error cases (#95)

* Add Unit  Test for testing a corrupted config

* Add Unit Test for testing errors from .Stats()

* Refactor  Datafile into an interface and add Unit Tests for testing Merge() errors

* Refactor indexer into an interface and add Unit Tests for .Close() errors

* Add Unit Tests for .Delete() errors

* Add Unit Tests for  testing Put/Get errors

* Add Unit Test for testing Open errors (bad path for example)

* Refactor out bitcask.writeConfig

* Add more tests for config errors

* Add unit test for options that might error

* Add more test cases for close errors

* Add test case for rotating datafiles

* Fix a possible data race in .Stats()

* Add test case for checksum errors

* Add test case for Sync errors with Put and WithSync enabled

* Refactor and use testify.mock for mocks and generate mocks for all interfaces

* Refactor TestCloseErrors

* Refactored TestDeleteErrors

* Refactored TestGetErrors

* Refactored TestPutErrors

* Refactored TestMergeErrors and fixed a bug with .Fold()

* Add test case for Scan() errors

* Apparently only Scan() can return nil Node()s?

internal/index/codec_index.go

@@ -108,8 +108,7 @@ func readIndex(r io.Reader, t art.Tree, maxKeySize int) error {
 	return nil
 }
 
-// WriteIndex persists a Tree into a io.Writer
-func WriteIndex(t art.Tree, w io.Writer) (err error) {
+func writeIndex(t art.Tree, w io.Writer) (err error) {
 	t.ForEach(func(node art.Node) bool {
 		err = writeBytes(node.Key(), w)
 		if err != nil {

internal/index/index.go

@@ -2,26 +2,55 @@ package index
 
 import (
 	"os"
-	"path"
 
 	art "github.com/plar/go-adaptive-radix-tree"
 	"github.com/prologic/bitcask/internal"
 )
 
-// ReadFromFile reads an index from a persisted file
-func ReadFromFile(filePath string, maxKeySize int) (art.Tree, bool, error) {
+type Indexer interface {
+	Load(path string, maxkeySize int) (art.Tree, bool, error)
+	Save(t art.Tree, path string) error
+}
+
+func NewIndexer() Indexer {
+	return &indexer{}
+}
+
+type indexer struct{}
+
+func (i *indexer) Load(path string, maxKeySize int) (art.Tree, bool, error) {
 	t := art.New()
-	if !internal.Exists(path.Join(filePath, "index")) {
+
+	if !internal.Exists(path) {
 		return t, false, nil
 	}
 
-	f, err := os.Open(path.Join(filePath, "index"))
+	f, err := os.Open(path)
 	if err != nil {
 		return t, true, err
 	}
 	defer f.Close()
+
 	if err := readIndex(f, t, maxKeySize); err != nil {
 		return t, true, err
 	}
 	return t, true, nil
 }
+
+func (i *indexer) Save(t art.Tree, path string) error {
+	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if err := writeIndex(t, f); err != nil {
+		return err
+	}
+
+	if err := f.Sync(); err != nil {
+		return err
+	}
+
+	return f.Close()
+}