added two new testcases for backoff.go

backoff_test.go

@@ -1,6 +1,10 @@
 package grpc
 
-import "testing"
+import ( 
+	"testing"
+	"math/rand"
+	"time"
+)
 
 func TestBackoffConfigDefaults(t *testing.T) {
 	b := BackoffConfig{}
@@ -9,3 +13,36 @@ func TestBackoffConfigDefaults(t *testing.T) {
 		t.Fatalf("expected BackoffConfig to pickup default parameters: %v != %v", b, DefaultBackoffConfig)
 	}
 }
+
+func TestBackoffWitDifferentNumberOfRetries(t *testing.T) {
+	const MAX_RETRIES = 10
+	randSrc := rand.NewSource(time.Now().UnixNano())
+	randGen := rand.New(randSrc)
+	for i := 0; i < 5; i++ {
+		// generate a randon number, between 0 and MAX_RETRIES, to be used as number of retries
+		retries := randGen.Intn(MAX_RETRIES)
+		b := BackoffConfig{}
+		setDefaults(&b)
+		backoffTime := b.backoff(retries)
+		// backoff time should be between basedelay and max delay
+		if backoffTime < b.baseDelay || backoffTime > b.MaxDelay {
+			t.Fatalf("expected backoff time: %v to be between basedelay: %v and maxdelay: %v",backoffTime,b.baseDelay,b.MaxDelay)
+		}
+	}
+}
+
+func TestBackOffTimeIncreasesWithRetries(t *testing.T) {
+	const MAX_RETRIES = 10
+	b := BackoffConfig{}
+	setDefaults(&b)
+	// base delay
+	lastBackOffTime := b.backoff(0)
+	for retries := 1; retries <= MAX_RETRIES; retries++ {
+		backoffTime := b.backoff(retries)
+		// backoff time should increase as number of retries increase
+		if backoffTime <= lastBackOffTime {
+			t.Fatalf("backoffTime for %v retries : %v is smaller than backoffTime for %v retries: %v",retries,backoffTime,retries-1,lastBackOffTime)
+		}
+		lastBackOffTime = backoffTime
+	}
+}