fix: increase the possible random numbers used for stickiness id (#241)

This update changes how we calculate random percentages in the SDK. Instead of multiplying a random int with 100 (which absolutely could cause overflows), we now use a ranged `Next` call, to generate one of 10k different numbers. This is in line with how we get the random number in other sdks.

I've added a test to ensure that random distribution works to within the accepted deviation.

src/Unleash/Strategies/FlexibleRolloutStrategy.cs

@@ -15,7 +15,7 @@ public class FlexibleRolloutStrategy : IStrategy
  public FlexibleRolloutStrategy()
  {
  var random = new Random();
- randomGenerator = () => (random.Next() * 100).ToString();
+ randomGenerator = () => random.Next(1, 10001).ToString();
  }
 
  public FlexibleRolloutStrategy(Func<string> randomGenerator)

tests/Unleash.Tests/Strategy/FlexibleRolloutStrategyTest.cs

@@ -361,5 +361,43 @@ public void Should_be_enabled_for_empty_userid()
  // Assert
  enabled.Should().BeTrue();
  }
+
+ [Test]
+ public void Should_only_at_most_miss_by_one_percent()
+ {
+ // Arrange
+ var strategy = new FlexibleRolloutStrategy();
+ var percentage = 25;
+ var groupId = "groupId";
+ var rounds = 200_000;
+ var enabledCount = 0;
+
+ // Act
+ for (int i = 0; i < rounds; i++)
+ {
+ var parameters = new Dictionary<string, string>
+ {
+ { "rollout", percentage.ToString() },
+ { "groupId", groupId }
+ };
+ var context = new UnleashContext
+ {
+ SessionId = i.ToString()
+ };
+
+ if (strategy.IsEnabled(parameters, context))
+ {
+ enabledCount++;
+ }
+ }
+
+ var actualPercentage = (int)Math.Round((enabledCount / (double)rounds) * 100);
+ var highMark = percentage + 1;
+ var lowMark = percentage - 1;
+
+ // Assert
+ actualPercentage.Should().BeGreaterOrEqualTo(lowMark);
+ actualPercentage.Should().BeLessOrEqualTo(highMark);
+ }
  }
 }