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Feature #16655

Updated by ko1 (Koichi Sasada) 6 months ago

# Points 

 * call `srand($seed)` before each test. `$seed` is given seed number by `--seed N` 

 # Background 

 Some tests use `rand()` to produce random number to generate random test examples. 

 Example:  

 ``` 
   def test_local_variable_set_wb 
     assert_ruby_status([], <<-'end;', '[Bug #13605]', timeout: 30) 
       b = binding 
       n = 20_000 

       n.times do |i| 
         v = rand(2_000) 
         name = "n#{v}" 
         value = Object.new 
         b.local_variable_set name, value 
       end 
     end; 
   end 
 ``` 

 This test generates 2,000 randomly named ivar which point random numbers. 

 However, several tests calls `srand(0)` and this random sequence is affected by test methods order. 

 Two problems: 

 * Test authors of this kind of tests should assume that every test processes uses very different random sequence to increase the test coverage. 
 * We can not get reproducible results on such tests which use random sequence with `--seed` because of `srand(0)` using tests. 

 # Proposal 

 To solve the above two problems, I'll I`ll insert `srand($seed)` at the beginning of each test (`$seed` is given by `--seed` option). 
 This proposal respects `--seed` option more, so we can expect more deterministic results. 

 I measured performance overhead and I can't get meaningful slow down. 

 # Additional note 

 Surprisingly, `--seed` option is ignored just now on test-all, so I'll fix this problem too. 

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