Add unit-test for FairLeaseGovernor (#149)

I had written this test for PR #147, but failed to add it.

Author: stevegury

reactivesocket-core/src/test/java/io/reactivesocket/lease/FairLeaseGovernorTest.java

@@ -0,0 +1,51 @@
+package io.reactivesocket.lease;
+
+import io.reactivesocket.Frame;
+import io.reactivesocket.internal.Responder;
+import org.junit.Test;
+
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.mock;
+
+public class FairLeaseGovernorTest {
+
+    @Test(timeout = 10_000L)
+    public void testAcceptRefuseLease() throws InterruptedException {
+        int n = 10;
+        FairLeaseGovernor governor = new FairLeaseGovernor(n, 100, TimeUnit.MILLISECONDS);
+        Responder responder = mock(Responder.class);
+        Frame frame = mock(Frame.class);
+
+        governor.register(responder);
+        Thread.sleep(10);
+
+        assertTrue("First request is accepted", governor.accept(responder, frame));
+        for (int i = 1; i < n; i++) {
+            assertTrue("Subsequent requests are accepted", governor.accept(responder, frame));
+        }
+        assertFalse("11th request is refused", governor.accept(responder, frame));
+
+        Thread.sleep(100);
+        assertTrue("After some time, requests are accepted again", governor.accept(responder, frame));
+    }
+
+    @Test(timeout = 1000_000L)
+    public void testLeaseFairness() throws InterruptedException {
+        FairLeaseGovernor governor = new FairLeaseGovernor(4, 1000, TimeUnit.MILLISECONDS);
+        Responder responder1 = mock(Responder.class);
+        Responder responder2 = mock(Responder.class);
+        Frame frame = mock(Frame.class);
+
+        governor.register(responder1);
+        governor.register(responder2);
+        Thread.sleep(10);
+
+        assertTrue("First request is accepted on responder 1", governor.accept(responder1, frame));
+        assertTrue("First request is accepted on responder 2", governor.accept(responder2, frame));
+        assertTrue("Second request is accepted on responder 1", governor.accept(responder1, frame));
+        assertFalse("Third request is refused on responder 1", governor.accept(responder1, frame));
+        assertTrue("Second request is accepted on responder 2", governor.accept(responder2, frame));
+    }
+}