Ensure global gitignore file is not loaded in tests

tools/ignorefiles/api.go

@@ -10,6 +10,7 @@ import (
 var _ = fmt.Print
 
 type IgnoreFile interface {
+	Len() int // number of rules
 	LoadString(string) error
 	LoadBytes([]byte) error
 	LoadLines(...string) error

tools/ignorefiles/gitignore.go

@@ -29,6 +29,8 @@ type Gitignore struct {
 	line_number_offset         int
 }
 
+func (g Gitignore) Len() int { return len(g.patterns) }
+
 func (g Gitignore) IsIgnored(relpath string, ftype os.FileMode) (is_ignored bool, linenum_of_matching_rule int, pattern string) {
 	if os.PathSeparator != '/' {
 		relpath = strings.ReplaceAll(relpath, string(os.PathSeparator), "/")