Improved code quality

file.go

@@ -1,26 +0,0 @@
-package assert
-
-import (
-	"runtime/debug"
-	"strings"
-)
-
-// file returns the first line containing "_test.go" in the debug stack.
-func file() string {
-	stack := string(debug.Stack())
-	lines := strings.Split(stack, "\n")
-
-	for _, line := range lines {
-		if strings.Contains(line, "_test.go") {
-			space := strings.LastIndex(line, " ")
-
-			if space != -1 {
-				line = line[:space]
-			}
-
-			return strings.TrimSpace(line)
-		}
-	}
-
-	return ""
-}