property tests

gistfile1.lua

function test_encoding_and_decoding_should_be_lossless()
    assert_random({ name="encode_decode",
                    always={ -- regressions: always test these seeds
                        -- found test_encoding_N_zeroes's edge case
                        3735485075354, 2721442120304, 3956609256407,
                        -- found test_encoding_two_zeroes's edge case
                        175063139413, 3771894109384, 1972533966070},
                },
                  function ()
                      local ints = gen_int_array()
                      local packed = rle.encode(ints)
                      local unpacked = rle.decode(packed)
                      
                      local max = #ints > #unpacked and #ints or #unpacked
                      
                      for i=1,#ints do
                          assert_true(unpacked[i] == ints[i])
                      end
                  end)
end

function test_encoded_data_should_usually_decrease_in_size_or_stay_the_same()
    assert_random({ name="decrease" },
                  function ()
                      local ints = gen_int_array()
                      local packed = rle.encode(ints)
                      assert_true(#packed <= #ints)
                  end)
end

function test_encoding_multiple_times_quickly_reach_a_fixpoint()
    assert_random({ name="diminshing_returns" },
                  function ()
                      local prev = gen_int_array()
                      for count=1,5 do
                          local cur = rle.encode(prev)
                          if #cur >= #prev then return end
                          prev = cur
                      end
                      fail("still shrinking after 5 cycles")
                  end)
end

function test_encoded_values_should_not_have_long_runs_of_duplicate_values()
    assert_random({ name="decrease" },
                  function ()
                      local ints = gen_int_array()
                      local packed = rle.encode(ints)
                      local longest, cur_run, last = 0, 0, nil
                      for i=1,#packed do
                          if last and last == packed[i] then
                              cur_run = cur_run + 1
                          else
                              if cur_run > longest then
                                  longest = cur_run
                              end
                              cur_run = 0
                          end
                          last = packed[i]
                      end
                      assert_true(longest < 3)
                  end)
end