Refactor array test to use assert_xxx method

It is useful that we know exptecd and actual value when test fails to use assert_xxx method.

Ex:
Fail: Array#compact
 - Assertion[2] Failed: Expected to be equal
    Expected: [0, nil, "2", nil, :t, false, nil]
      Actual: [1, nil, "2", nil, :t, false, nil]
Total: 758
   OK: 757
   KO: 1