Fix commit_file_stats function (#926)

Fix commit_file_stats function

Author: ajnavarro

internal/function/commit_file_stats.go

@@ -66,7 +66,7 @@ func (f *CommitFileStats) WithChildren(children ...sql.Expression) (sql.Expressi
 		to = children[1]
 	}
 
-	return &CommitStats{repo, from, to}, nil
+	return &CommitFileStats{repo, from, to}, nil
 }
 
 // Children implements the Expression interface.

internal/function/commit_file_stats_test.go

@@ -2,6 +2,8 @@ package function
 
 import (
 	"context"
+
+	"reflect"
 	"testing"
 
 	"github.com/src-d/gitbase"
@@ -80,3 +82,17 @@ func TestCommitFileStats(t *testing.T) {
 		})
 	}
 }
+
+func TestWithChildren(t *testing.T) {
+	repo := expression.NewGetField(0, sql.Text, "repository_id", false)
+	from := expression.NewGetField(2, sql.Text, "commit_hash", false)
+
+	cfs, err := NewCommitFileStats(repo, from)
+	require.NoError(t, err)
+
+	newCfs, err := cfs.WithChildren(repo, from)
+
+	require.NoError(t, err)
+	require.EqualValues(t, cfs.Children(), newCfs.Children())
+	require.Equal(t, reflect.TypeOf(cfs), reflect.TypeOf(newCfs))
+}