fix backoff calucuration #245

src/test/java/io/socket/backo/BackoffTest.java

@@ -2,6 +2,9 @@ package io.socket.backo;
 
 import org.junit.Test;
 
+import java.math.BigDecimal;
+import java.math.BigInteger;
+
 import static org.junit.Assert.assertTrue;
 
 public class BackoffTest {
@@ -22,14 +25,23 @@ public class BackoffTest {
 
     @Test
     public void durationOverflow() {
-        Backoff b = new Backoff();
-        b.setMin(100);
-        b.setMax(10000);
-        b.setJitter(1.0);
+        for (int i = 0; i < 10; i++) {
+            Backoff b = new Backoff();
+            b.setMin(100);
+            b.setMax(10000);
+            b.setJitter(0.5);
 
-        for (int i = 0; i < 100; i++) {
-            long duration = b.duration();
-            assertTrue(100 <= duration && duration <= 10000);
+            // repeats to make it overflow (a long can have 2 ** 63 - 1)
+            for (int j = 0; j < 100; j++) {
+                BigInteger ms = BigInteger.valueOf(100).multiply(BigInteger.valueOf(2).pow(j));
+                BigInteger deviation = new BigDecimal(ms).multiply(BigDecimal.valueOf(0.5)).toBigInteger();
+                BigInteger duration = BigInteger.valueOf(b.duration());
+
+                BigInteger min = ms.subtract(deviation).min(BigInteger.valueOf(10000));
+                BigInteger max = ms.add(deviation).min(BigInteger.valueOf(10001));
+                assertTrue(min + " <= " + duration + " < " + max,
+                        min.compareTo(duration) <= 0 && max.compareTo(duration) == 1);
+            }
         }
     }
 }