Revert "Remove testnet-only difficulty rules"

This reverts commit 333ea3c426.

src/gtest/test_rpc.cpp

@@ -9,6 +9,33 @@
 #include "streams.h"
 #include "utilstrencodings.h"
 
+TEST(rpc, GetDifficultyTestnetRules) {
+    SelectParams(CBaseChainParams::TESTNET);
+
+    CBlockIndex prev;
+    prev.nTime = 1472700000;
+    prev.nBits = 0x201fffff;
+
+    CBlockIndex curr;
+    curr.pprev = &prev;
+    curr.nTime = 1472700300;
+    curr.nBits = 0x207fffff;
+
+    // Time interval is within 5 minutes, so the min-difficulty block should be
+    // interpreted as a valid network difficulty.
+    EXPECT_EQ(1, GetDifficulty(&curr));
+    EXPECT_EQ(1, GetNetworkDifficulty(&curr));
+
+    curr.nTime += 1;
+
+    // Time interval is over 5 minutes, so the min-difficulty block should be
+    // ignored for network difficulty determination.
+    EXPECT_EQ(1, GetDifficulty(&curr));
+    // We have to check this directly, because of some combination of rounding
+    // and truncation issues that result in Google Test displaying 4 != 4
+    EXPECT_EQ((double)0x7fffff/(double)0x1fffff, GetNetworkDifficulty(&curr));
+}
+
 extern UniValue blockToJSON(const CBlock& block, const CBlockIndex* blockindex, bool txDetails = false);
 
 TEST(rpc, check_blockToJSON_returns_minified_solution) {