Mutate values to improve code coverage

[Markoutte]

Description

Currently, we do some simple mutations that don't take into account the result of execution. We could try to remember values which increase coverage and try to mutate values inside to find more paths.

Expected behavior

For a given string "good" we should find all paths using mutations for this code:

if (str.charAt(0) == 'b')
  if (str.charAt(1) == 'a')
    if (str.charAt(2) == 'd')
      throw new Error();

Potential alternatives

Mutations can give nothing that it is OK if no new paths are found.

Context

Mutation is a technique that can find new paths by mutating already found values.