Add test harness for DB

[Fullstop000]

Part of #3

Signed-off-by: Fullstop000 [email protected]

[codecov]

Codecov Report

Merging #37 into master will increase coverage by 12.89%.
The diff coverage is 81.06%.

@@            Coverage Diff             @@
##           master     #37       +/-   ##
==========================================
+ Coverage    63.2%   76.1%   +12.89%     
==========================================
  Files          34      34               
  Lines        6493    6737      +244     
==========================================
+ Hits         4104    5127     +1023     
+ Misses       2389    1610      -779

Impacted Files	Coverage Δ
src/compaction.rs	6.15% <ø> (+6.15%)	⬆️
src/record/mod.rs	97.98% <ø> (-0.02%)	⬇️
src/version/version_edit.rs	86.15% <ø> (+5.76%)	⬆️
src/record/writer.rs	96.82% <ø> (+4.63%)	⬆️
src/sstable/mod.rs	88.06% <0%> (+0.09%)	⬆️
src/sstable/filter_block.rs	96% <100%> (+0.02%)	⬆️
src/filter/bloom.rs	96.42% <100%> (ø)	⬆️
src/sstable/block.rs	98.04% <100%> (+0.01%)	⬆️
src/batch.rs	93.18% <100%> (+3.35%)	⬆️
src/storage/mem.rs	91.69% <100%> (+3.71%)	⬆️
... and 28 more

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