Fix ngt index path of test case (#2130)

* fix index path for test

Signed-off-by: hlts2 <hiroto.funakoshi.hiroto@gmail.com>

* use t.TempDir for index path

Signed-off-by: hlts2 <hiroto.funakoshi.hiroto@gmail.com>

* create inde temp directory and fix fails test

Signed-off-by: hlts2 <hiroto.funakoshi.hiroto@gmail.com>

* refactoring comprator

Signed-off-by: hlts2 <hiroto.funakoshi.hiroto@gmail.com>

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Signed-off-by: hlts2 <hiroto.funakoshi.hiroto@gmail.com>