diff --git a/tests/backoff_test.go b/tests/backoff_test.go
new file mode 100644
index 0000000..46450b9
--- /dev/null
+++ b/tests/backoff_test.go
@@ -0,0 +1,83 @@
+package taskqueue_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/KengoWada/taskqueue"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBackoffPolicy(t *testing.T) {
+	tests := []struct {
+		name          string
+		backoffPolicy *taskqueue.BackoffPolicy
+		retries       int
+		expectedDelay time.Duration
+		allowJitter   bool
+	}{
+		{
+			name: "retry one",
+			backoffPolicy: &taskqueue.BackoffPolicy{
+				BaseDelay: 1 * time.Millisecond,
+				MaxDelay:  10 * time.Millisecond,
+			},
+			retries:       1,
+			expectedDelay: 1 * time.Millisecond,
+		},
+		{
+			name: "retry three",
+			backoffPolicy: &taskqueue.BackoffPolicy{
+				BaseDelay: 1 * time.Millisecond,
+				MaxDelay:  10 * time.Millisecond,
+			},
+			retries:       3,
+			expectedDelay: 4 * time.Millisecond,
+		},
+		{
+			name: "max delay",
+			backoffPolicy: &taskqueue.BackoffPolicy{
+				BaseDelay: 5 * time.Millisecond,
+				MaxDelay:  10 * time.Millisecond,
+			},
+			retries:       5,
+			expectedDelay: 10 * time.Millisecond, // should not exceed MaxDelay
+		},
+		{
+			name: "jitter applied",
+			backoffPolicy: &taskqueue.BackoffPolicy{
+				BaseDelay:     1 * time.Millisecond,
+				MaxDelay:      10 * time.Millisecond,
+				UseJitter:     true,
+				JitterRangeMs: 5,
+			},
+			retries:       1,
+			expectedDelay: 1 * time.Millisecond, // with jitter this will vary slightly
+			allowJitter:   true,
+		},
+		{
+			name: "no jitter applied",
+			backoffPolicy: &taskqueue.BackoffPolicy{
+				BaseDelay: 1 * time.Millisecond,
+				MaxDelay:  10 * time.Millisecond,
+				UseJitter: false,
+			},
+			retries:       1,
+			expectedDelay: 1 * time.Millisecond,
+			allowJitter:   false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			delay := tt.backoffPolicy.Calculate(tt.retries)
+
+			if tt.allowJitter {
+				assert.GreaterOrEqual(t, delay, tt.expectedDelay)
+				assert.LessOrEqual(t, delay, tt.expectedDelay+5*time.Millisecond)
+			} else {
+				assert.Equal(t, delay, tt.expectedDelay)
+			}
+		})
+	}
+}
diff --git a/tests/utils.go b/tests/utils_test.go
similarity index 100%
rename from tests/utils.go
rename to tests/utils_test.go