Add unit tests for next difficulty calculations

Split GetNextWorkRequired() into two functions to allow the difficulty calculations to
be tested without requiring a full blockchain.
Add unit tests to cover basic difficulty calculation, plus each of the min/max actual
time, and maximum difficulty target conditions.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/pow.cpp b/src/pow.cpp
index 6dd5c4c12c..b75b293c90 100644
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -48,8 +48,13 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
         pindexFirst = pindexFirst->pprev;
     assert(pindexFirst);
 
+    return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime());
+}
+
+unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime)
+{
     // Limit adjustment step
-    int64_t nActualTimespan = pindexLast->GetBlockTime() - pindexFirst->GetBlockTime();
+    int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime;
     LogPrintf("  nActualTimespan = %d  before bounds\n", nActualTimespan);
     if (nActualTimespan < Params().TargetTimespan()/4)
         nActualTimespan = Params().TargetTimespan()/4;