Add tests for Config structure

config.go

@@ -1,6 +1,7 @@
 package tusd
 
 import (
+	"errors"
 	"log"
 	"net/url"
 	"os"
@@ -56,8 +57,13 @@ func (config *Config) validate() error {
 
 	if config.StoreComposer == nil {
 		config.StoreComposer = newStoreComposerFromDataStore(config.DataStore)
+		config.DataStore = nil
 	} else if config.DataStore != nil {
-		// TODO: consider returning an error
+		return errors.New("tusd: either StoreComposer or DataStore may be set in Config, but not both")
+	}
+
+	if config.StoreComposer.Core == nil {
+		return errors.New("tusd: StoreComposer in Config needs to contain a non-nil core")
 	}
 
 	return nil

config_test.go

@@ -0,0 +1,58 @@
+package tusd
+
+import (
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type zeroStore struct{}
+
+func (store zeroStore) NewUpload(info FileInfo) (string, error) {
+	return "", nil
+}
+func (store zeroStore) WriteChunk(id string, offset int64, src io.Reader) (int64, error) {
+	return 0, nil
+}
+
+func (store zeroStore) GetInfo(id string) (FileInfo, error) {
+	return FileInfo{}, nil
+}
+
+func TestConfig(t *testing.T) {
+	a := assert.New(t)
+
+	config := Config{
+		DataStore: zeroStore{},
+		BasePath:  "files",
+	}
+
+	a.Nil(config.validate())
+	a.NotNil(config.Logger)
+	a.NotNil(config.StoreComposer)
+	a.Equal("/files/", config.BasePath)
+}
+
+func TestConfigEmptyCore(t *testing.T) {
+	a := assert.New(t)
+
+	config := Config{
+		StoreComposer: NewStoreComposer(),
+	}
+
+	a.Error(config.validate())
+}
+
+func TestConfigStoreAndComposer(t *testing.T) {
+	a := assert.New(t)
+	composer := NewStoreComposer()
+	composer.UseCore(zeroStore{})
+
+	config := Config{
+		StoreComposer: composer,
+		DataStore:     zeroStore{},
+	}
+
+	a.Error(config.validate())
+}

cors_test.go

@@ -8,7 +8,11 @@ import (
 )
 
 func TestCORS(t *testing.T) {
-	handler, _ := NewHandler(Config{})
+	store := NewStoreComposer()
+	store.UseCore(zeroStore{})
+	handler, _ := NewHandler(Config{
+		StoreComposer: store,
+	})
 
 	(&httpTest{
 		Name:   "Preflight request",

options_test.go

@@ -8,8 +8,11 @@ import (
 )
 
 func TestOptions(t *testing.T) {
+	store := NewStoreComposer()
+	store.UseCore(zeroStore{})
 	handler, _ := NewHandler(Config{
-		MaxSize: 400,
+		StoreComposer: store,
+		MaxSize:       400,
 	})
 
 	(&httpTest{