Add unit tests to verify how current and previous block time and difficulty are extracted from blocks

src/main/java/org/libdohj/params/AbstractDogecoinParams.java

@@ -210,14 +210,25 @@ public abstract class AbstractDogecoinParams extends NetworkParameters implement
 
         Block blockIntervalAgo = cursor.getHeader();
         long receivedTargetCompact = nextBlock.getDifficultyTarget();
-        long newTargetCompact = this.getNewDifficultyTarget(previousHeight, prev.getTimeSeconds(),
+        long newTargetCompact = this.getNewDifficultyTarget(previousHeight, prev, blockIntervalAgo);
-            prev.getDifficultyTarget(), blockIntervalAgo.getTimeSeconds());
 
         if (newTargetCompact != receivedTargetCompact)
             throw new VerificationException("Network provided difficulty bits do not match what was calculated: " +
                     newTargetCompact + " vs " + receivedTargetCompact);
     }
 
+    /**
+     * 
+     * @param prev the block immediately before the retarget block.
+     * @param blockIntervalAgo The last retarget block.
+     * @return New difficulty target as compact bytes.
+     */
+    public long getNewDifficultyTarget(int previousHeight, final Block prev,
+        final Block blockIntervalAgo) {
+        return this.getNewDifficultyTarget(previousHeight, prev.getTimeSeconds(),
+            blockIntervalAgo.getDifficultyTarget(), blockIntervalAgo.getTimeSeconds());
+    }
+
     /**
      * 
      * @param previousHeight Height of the block immediately previous to the one we're calculating difficulty of.

src/test/java/org/libdohj/params/AbstractDogecoinParamsTest.java

@@ -15,10 +15,14 @@
  */
 package org.libdohj.params;
 
-import org.libdohj.params.AbstractDogecoinParams;
+import java.io.IOException;
-import org.libdohj.params.DogecoinMainNetParams;
+import org.bitcoinj.core.AltcoinBlock;
+import org.bitcoinj.core.Context;
+import org.bitcoinj.core.Util;
 import static org.junit.Assert.assertEquals;
+import org.junit.Before;
 import org.junit.Test;
+import org.libdohj.core.AltcoinSerializer;
 
 /**
  *
@@ -27,6 +31,11 @@ import org.junit.Test;
 public class AbstractDogecoinParamsTest {
     private static final AbstractDogecoinParams params = DogecoinMainNetParams.get();
 
+    @Before
+    public void setUp() throws Exception {
+        Context context = new Context(params);
+    }
+
     @Test
     public void shouldCalculateBitcoinLikeDifficulty() {
         int previousHeight = 239;
@@ -36,13 +45,6 @@ public class AbstractDogecoinParamsTest {
         long newDifficulty = params.getNewDifficultyTarget(previousHeight, previousBlockTime, lastRetargetDifficulty, lastRetargetTime);
         assertEquals(newDifficulty, 0x1e00ffff);
 
-        previousHeight = 479;
-        previousBlockTime = 1386475840;
-        lastRetargetDifficulty = 0x1e0fffff;
-        lastRetargetTime = 1386475638; // Block 239
-        newDifficulty = params.getNewDifficultyTarget(previousHeight, previousBlockTime, lastRetargetDifficulty, lastRetargetTime);
-        assertEquals(newDifficulty, 0x1e00ffff);
-
         previousHeight = 9599;
         previousBlockTime = 1386954113;
         lastRetargetDifficulty = 0x1c1a1206;
@@ -71,4 +73,18 @@ public class AbstractDogecoinParamsTest {
         long newDifficulty = params.getNewDifficultyTarget(previousHeight, previousBlockTime, lastRetargetDifficulty, lastRetargetTime);
         assertEquals(newDifficulty, 0x1b6558a4);
     }
+
+    @Test
+    public void shouldCalculateFirstRetarget() throws IOException {
+        // Do a more in-depth test for the first retarget
+        byte[] payload = Util.getBytes(getClass().getResourceAsStream("dogecoin_block239.bin"));
+        AltcoinSerializer serializer = (AltcoinSerializer)params.getDefaultSerializer();
+        final AltcoinBlock block239 = (AltcoinBlock)serializer.makeBlock(payload);
+        final AltcoinBlock block479;
+
+        payload = Util.getBytes(getClass().getResourceAsStream("dogecoin_block479.bin"));
+        block479 = (AltcoinBlock)serializer.makeBlock(payload);
+
+        assertEquals(0x1e00ffff, params.getNewDifficultyTarget(479, block239, block479));
+    }
 }