Implement Size() in mock connector (#974)

## Description

Adds the ability to use mockconnector for onedrive and exchange restores, reducing potential code duplication overall.

## Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🐹 Trivial/Minor

## Issue(s)

* #913 

## Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

src/internal/connector/mockconnector/mock_data_collection.go

@@ -26,6 +26,7 @@ var (
 	_ data.Collection = &MockExchangeDataCollection{}
 	_ data.Stream     = &MockExchangeData{}
 	_ data.StreamInfo = &MockExchangeData{}
+	_ data.StreamSize = &MockExchangeData{}
 )
 
 // NewMockExchangeDataCollection creates an data collection that will return the specified number of
@@ -63,6 +64,7 @@ func (medc *MockExchangeDataCollection) Items() <-chan data.Stream {
 			res <- &MockExchangeData{
 				ID:     medc.Names[i],
 				Reader: io.NopCloser(bytes.NewReader(medc.Data[i])),
+				size:   int64(len(medc.Data[i])),
 			}
 		}
 	}()
@@ -75,6 +77,7 @@ type MockExchangeData struct {
 	ID      string
 	Reader  io.ReadCloser
 	ReadErr error
+	size    int64
 }
 
 func (med *MockExchangeData) UUID() string {
@@ -99,6 +102,10 @@ func (med *MockExchangeData) Info() details.ItemInfo {
 	}
 }
 
+func (med *MockExchangeData) Size() int64 {
+	return med.size
+}
+
 // GetMockMessageBytes returns bytes for Messageable item.
 // Contents verified as working with sample data from kiota-serialization-json-go v0.5.5
 func GetMockMessageBytes(subject string) []byte {

src/internal/connector/mockconnector/mock_data_collection_test.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/alcionai/corso/src/internal/connector/mockconnector"
 	"github.com/alcionai/corso/src/internal/connector/support"
+	"github.com/alcionai/corso/src/internal/data"
 )
 
 type MockExchangeCollectionSuite struct {
@@ -37,6 +38,22 @@ func (suite *MockExchangeCollectionSuite) TestMockExchangeCollection() {
 	assert.Equal(suite.T(), 2, messagesRead)
 }
 
+func (suite *MockExchangeCollectionSuite) TestMockExchangeCollectionItemSize() {
+	t := suite.T()
+	mdc := mockconnector.NewMockExchangeCollection(nil, 2)
+
+	mdc.Data[1] = []byte("This is some buffer of data so that the size is different than the default")
+
+	for item := range mdc.Items() {
+		buf, err := ioutil.ReadAll(item.ToReader())
+		assert.NoError(t, err)
+
+		assert.Implements(t, (*data.StreamSize)(nil), item)
+		s := item.(data.StreamSize)
+		assert.Equal(t, int64(len(buf)), s.Size())
+	}
+}
+
 // NewExchangeCollectionMail_Hydration tests that mock exchange mail data collection can be used for restoration
 // functions by verifying no failures on (de)serializing steps using kiota serialization library
 func (suite *MockExchangeCollectionSuite) TestMockExchangeCollection_NewExchangeCollectionMail_Hydration() {
@@ -64,7 +81,7 @@ func TestMockExchangeDataSuite(t *testing.T) {
 }
 
 func (suite *MockExchangeDataSuite) TestMockExchangeData() {
-	data := []byte("foo")
+	itemData := []byte("foo")
 	id := "bar"
 
 	table := []struct {
@@ -76,7 +93,7 @@ func (suite *MockExchangeDataSuite) TestMockExchangeData() {
 			name: "NoError",
 			reader: &mockconnector.MockExchangeData{
 				ID:     id,
-				Reader: io.NopCloser(bytes.NewReader(data)),
+				Reader: io.NopCloser(bytes.NewReader(itemData)),
 			},
 			check: require.NoError,
 		},
@@ -100,7 +117,7 @@ func (suite *MockExchangeDataSuite) TestMockExchangeData() {
 				return
 			}
 
-			assert.Equal(t, data, buf)
+			assert.Equal(t, itemData, buf)
 		})
 	}
 }