docstore/mongodocstore: Make TestLowerCaseFields re-runnable

docstore/mongodocstore/mongo_test.go

@@ -21,6 +21,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"testing"
 	"time"
 
@@ -236,6 +237,25 @@ func TestLowercaseFields(t *testing.T) {
 	}
 	coll := docstore.NewCollection(dc)
 	defer coll.Close()
+	defer func() {
+		// Delete all items in the collection.
+		iter := coll.Query().Get(ctx)
+		dels := coll.Actions()
+		for {
+			doc := map[string]interface{}{}
+			err := iter.Next(ctx, doc)
+			if err == io.EOF {
+				break
+			}
+			if err != nil {
+				t.Fatalf("%+v", err)
+			}
+			dels.Delete(doc)
+		}
+		if err := dels.Do(ctx); err != nil {
+			t.Fatalf("%+v", err)
+		}
+	}()
 
 	type S struct {
 		ID, F, G         int