Use NewServer and NewTLSServer instead of httptest.*

[k1LoW]

Fix test

[github-actions]

Code Metrics Report

	main (a03090a)	#9 (c43a180)	+/-
Coverage	61.9%	90.5%	+28.6%
Code to Test Ratio	1:4.5	1:5.1	+0.6
Test Execution Time	23s	13s	-10s

Details

  |                     | main (a03090a) | #9 (c43a180) |  +/-   |
  |---------------------|----------------|--------------|--------|
+ | Coverage            |          61.9% |        90.5% | +28.6% |
  |   Files             |              1 |            1 |      0 |
  |   Lines             |             21 |           21 |      0 |
+ |   Covered           |             13 |           19 |     +6 |
+ | Code to Test Ratio  |          1:4.5 |        1:5.1 |   +0.6 |
  |   Code              |             95 |           95 |      0 |
+ |   Test              |            427 |          484 |    +57 |
+ | Test Execution Time |            23s |          13s |   -10s |

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Reported by octocov