[PM 26682]milestone 2d display discount on subscription page (#6542)

* The discount badge implementation

* Address the claude pr comments

* Add more unit testing

* Add more test

* used existing flag

* Add the coupon Ids

* Add more code documentation

* Add some recommendation from claude

* Fix addition comments and prs

* Add more integration test

* Fix some comment and add more test

* rename the test methods

* Add more unit test and comments

* Resolve the null issues

* Add more test

* reword the comments

* Rename Variable

* Some code refactoring

* Change the coupon ID to milestone-2c

* Fix the failing Test

test/Core.Test/Models/Business/BillingCustomerDiscountTests.cs

@@ -0,0 +1,497 @@
+using Bit.Core.Models.Business;
+using Bit.Test.Common.AutoFixture.Attributes;
+using Stripe;
+using Xunit;
+
+namespace Bit.Core.Test.Models.Business;
+
+public class BillingCustomerDiscountTests
+{
+    [Theory]
+    [BitAutoData]
+    public void Constructor_PercentageDiscount_SetsIdActivePercentOffAndAppliesTo(string couponId)
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 25.5m,
+                AmountOff = null,
+                AppliesTo = new CouponAppliesTo
+                {
+                    Products = new List<string> { "product1", "product2" }
+                }
+            },
+            End = null // Active discount
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Equal(couponId, result.Id);
+        Assert.True(result.Active);
+        Assert.Equal(25.5m, result.PercentOff);
+        Assert.Null(result.AmountOff);
+        Assert.NotNull(result.AppliesTo);
+        Assert.Equal(2, result.AppliesTo.Count);
+        Assert.Contains("product1", result.AppliesTo);
+        Assert.Contains("product2", result.AppliesTo);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_AmountDiscount_ConvertsFromCentsToDollars(string couponId)
+    {
+        // Arrange - Stripe sends 1400 cents for $14.00
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = null,
+                AmountOff = 1400, // 1400 cents
+                AppliesTo = new CouponAppliesTo
+                {
+                    Products = new List<string>()
+                }
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Equal(couponId, result.Id);
+        Assert.True(result.Active);
+        Assert.Null(result.PercentOff);
+        Assert.Equal(14.00m, result.AmountOff); // Converted to dollars
+        Assert.NotNull(result.AppliesTo);
+        Assert.Empty(result.AppliesTo);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_InactiveDiscount_SetsActiveToFalse(string couponId)
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 15m
+            },
+            End = DateTime.UtcNow.AddDays(-1) // Expired discount
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Equal(couponId, result.Id);
+        Assert.False(result.Active);
+        Assert.Equal(15m, result.PercentOff);
+    }
+
+    [Fact]
+    public void Constructor_NullCoupon_SetsDiscountPropertiesToNull()
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = null,
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Null(result.Id);
+        Assert.True(result.Active);
+        Assert.Null(result.PercentOff);
+        Assert.Null(result.AmountOff);
+        Assert.Null(result.AppliesTo);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_NullAmountOff_SetsAmountOffToNull(string couponId)
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 10m,
+                AmountOff = null
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Null(result.AmountOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_ZeroAmountOff_ConvertsCorrectly(string couponId)
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                AmountOff = 0
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Equal(0m, result.AmountOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_LargeAmountOff_ConvertsCorrectly(string couponId)
+    {
+        // Arrange - $100.00 discount
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                AmountOff = 10000 // 10000 cents = $100.00
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Equal(100.00m, result.AmountOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_SmallAmountOff_ConvertsCorrectly(string couponId)
+    {
+        // Arrange - $0.50 discount
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                AmountOff = 50 // 50 cents = $0.50
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Equal(0.50m, result.AmountOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_BothDiscountTypes_SetsPercentOffAndAmountOff(string couponId)
+    {
+        // Arrange - Coupon with both percentage and amount (edge case)
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 20m,
+                AmountOff = 500 // $5.00
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Equal(20m, result.PercentOff);
+        Assert.Equal(5.00m, result.AmountOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_WithNullAppliesTo_SetsAppliesToNull(string couponId)
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 10m,
+                AppliesTo = null
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Null(result.AppliesTo);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_WithNullProductsList_SetsAppliesToNull(string couponId)
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 10m,
+                AppliesTo = new CouponAppliesTo
+                {
+                    Products = null
+                }
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Null(result.AppliesTo);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_WithDecimalAmountOff_RoundsCorrectly(string couponId)
+    {
+        // Arrange - 1425 cents = $14.25
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                AmountOff = 1425
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Equal(14.25m, result.AmountOff);
+    }
+
+    [Fact]
+    public void Constructor_DefaultConstructor_InitializesAllPropertiesToNullOrFalse()
+    {
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount();
+
+        // Assert
+        Assert.Null(result.Id);
+        Assert.False(result.Active);
+        Assert.Null(result.PercentOff);
+        Assert.Null(result.AmountOff);
+        Assert.Null(result.AppliesTo);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_WithFutureEndDate_SetsActiveToFalse(string couponId)
+    {
+        // Arrange - Discount expires in the future
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 20m
+            },
+            End = DateTime.UtcNow.AddDays(30) // Expires in 30 days
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.False(result.Active); // Should be inactive because End is not null
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_WithPastEndDate_SetsActiveToFalse(string couponId)
+    {
+        // Arrange - Discount already expired
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 20m
+            },
+            End = DateTime.UtcNow.AddDays(-30) // Expired 30 days ago
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.False(result.Active); // Should be inactive because End is not null
+    }
+
+    [Fact]
+    public void Constructor_WithNullCouponId_SetsIdToNull()
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = null,
+                PercentOff = 20m
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Null(result.Id);
+        Assert.True(result.Active);
+        Assert.Equal(20m, result.PercentOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_WithNullPercentOff_SetsPercentOffToNull(string couponId)
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = null,
+                AmountOff = 1000
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.Null(result.PercentOff);
+        Assert.Equal(10.00m, result.AmountOff);
+    }
+
+    [Fact]
+    public void Constructor_WithCompleteStripeDiscount_MapsAllProperties()
+    {
+        // Arrange - Comprehensive test with all Stripe Discount properties set
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = "premium_discount_2024",
+                PercentOff = 25m,
+                AmountOff = 1500, // $15.00
+                AppliesTo = new CouponAppliesTo
+                {
+                    Products = new List<string> { "prod_premium", "prod_family", "prod_teams" }
+                }
+            },
+            End = null // Active
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert - Verify all properties mapped correctly
+        Assert.Equal("premium_discount_2024", result.Id);
+        Assert.True(result.Active);
+        Assert.Equal(25m, result.PercentOff);
+        Assert.Equal(15.00m, result.AmountOff);
+        Assert.NotNull(result.AppliesTo);
+        Assert.Equal(3, result.AppliesTo.Count);
+        Assert.Contains("prod_premium", result.AppliesTo);
+        Assert.Contains("prod_family", result.AppliesTo);
+        Assert.Contains("prod_teams", result.AppliesTo);
+    }
+
+    [Fact]
+    public void Constructor_WithMinimalStripeDiscount_HandlesNullsGracefully()
+    {
+        // Arrange - Minimal Stripe Discount with most properties null
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = null,
+                PercentOff = null,
+                AmountOff = null,
+                AppliesTo = null
+            },
+            End = DateTime.UtcNow.AddDays(10) // Has end date
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert - Should handle all nulls gracefully
+        Assert.Null(result.Id);
+        Assert.False(result.Active);
+        Assert.Null(result.PercentOff);
+        Assert.Null(result.AmountOff);
+        Assert.Null(result.AppliesTo);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public void Constructor_WithEmptyProductsList_PreservesEmptyList(string couponId)
+    {
+        // Arrange
+        var discount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = couponId,
+                PercentOff = 10m,
+                AppliesTo = new CouponAppliesTo
+                {
+                    Products = new List<string>() // Empty but not null
+                }
+            },
+            End = null
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingCustomerDiscount(discount);
+
+        // Assert
+        Assert.NotNull(result.AppliesTo);
+        Assert.Empty(result.AppliesTo);
+    }
+}

test/Core.Test/Models/Business/SubscriptionInfoTests.cs

@@ -0,0 +1,125 @@
+using Bit.Core.Models.Business;
+using Stripe;
+using Xunit;
+
+namespace Bit.Core.Test.Models.Business;
+
+public class SubscriptionInfoTests
+{
+    [Fact]
+    public void BillingSubscriptionItem_NullPlan_HandlesGracefully()
+    {
+        // Arrange - SubscriptionItem with null Plan
+        var subscriptionItem = new SubscriptionItem
+        {
+            Plan = null,
+            Quantity = 1
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingSubscription.BillingSubscriptionItem(subscriptionItem);
+
+        // Assert - Should handle null Plan gracefully
+        Assert.Null(result.ProductId);
+        Assert.Null(result.Name);
+        Assert.Equal(0m, result.Amount); // Defaults to 0 when Plan is null
+        Assert.Null(result.Interval);
+        Assert.Equal(1, result.Quantity);
+        Assert.False(result.SponsoredSubscriptionItem);
+        Assert.False(result.AddonSubscriptionItem);
+    }
+
+    [Fact]
+    public void BillingSubscriptionItem_NullAmount_SetsToZero()
+    {
+        // Arrange - SubscriptionItem with Plan but null Amount
+        var subscriptionItem = new SubscriptionItem
+        {
+            Plan = new Plan
+            {
+                ProductId = "prod_test",
+                Nickname = "Test Plan",
+                Amount = null, // Null amount
+                Interval = "month"
+            },
+            Quantity = 1
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingSubscription.BillingSubscriptionItem(subscriptionItem);
+
+        // Assert - Should default to 0 when Amount is null
+        Assert.Equal("prod_test", result.ProductId);
+        Assert.Equal("Test Plan", result.Name);
+        Assert.Equal(0m, result.Amount); // Business rule: defaults to 0 when null
+        Assert.Equal("month", result.Interval);
+        Assert.Equal(1, result.Quantity);
+    }
+
+    [Fact]
+    public void BillingSubscriptionItem_ZeroAmount_PreservesZero()
+    {
+        // Arrange - SubscriptionItem with Plan and zero Amount
+        var subscriptionItem = new SubscriptionItem
+        {
+            Plan = new Plan
+            {
+                ProductId = "prod_test",
+                Nickname = "Test Plan",
+                Amount = 0, // Zero amount (0 cents)
+                Interval = "month"
+            },
+            Quantity = 1
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingSubscription.BillingSubscriptionItem(subscriptionItem);
+
+        // Assert - Should preserve zero amount
+        Assert.Equal("prod_test", result.ProductId);
+        Assert.Equal("Test Plan", result.Name);
+        Assert.Equal(0m, result.Amount); // Zero amount preserved
+        Assert.Equal("month", result.Interval);
+    }
+
+    [Fact]
+    public void BillingUpcomingInvoice_ZeroAmountDue_ConvertsToZero()
+    {
+        // Arrange - Invoice with zero AmountDue
+        // Note: Stripe's Invoice.AmountDue is non-nullable long, so we test with 0
+        // The null-coalescing operator (?? 0) in the constructor handles the case where
+        // ConvertFromStripeMinorUnits returns null, but since AmountDue is non-nullable,
+        // this test verifies the conversion path works correctly for zero values
+        var invoice = new Invoice
+        {
+            AmountDue = 0, // Zero amount due (0 cents)
+            Created = DateTime.UtcNow
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingUpcomingInvoice(invoice);
+
+        // Assert - Should convert zero correctly
+        Assert.Equal(0m, result.Amount);
+        Assert.NotNull(result.Date);
+    }
+
+    [Fact]
+    public void BillingUpcomingInvoice_ValidAmountDue_ConvertsCorrectly()
+    {
+        // Arrange - Invoice with valid AmountDue
+        var invoice = new Invoice
+        {
+            AmountDue = 2500, // 2500 cents = $25.00
+            Created = DateTime.UtcNow
+        };
+
+        // Act
+        var result = new SubscriptionInfo.BillingUpcomingInvoice(invoice);
+
+        // Assert - Should convert correctly
+        Assert.Equal(25.00m, result.Amount); // Converted from cents
+        Assert.NotNull(result.Date);
+    }
+}
+

test/Core.Test/Services/StripePaymentServiceTests.cs

@@ -3,6 +3,7 @@ using Bit.Core.Billing.Enums;
 using Bit.Core.Billing.Models.StaticStore.Plans;
 using Bit.Core.Billing.Pricing;
 using Bit.Core.Billing.Tax.Requests;
+using Bit.Core.Entities;
 using Bit.Core.Enums;
 using Bit.Core.Services;
 using Bit.Test.Common.AutoFixture;
@@ -515,4 +516,399 @@ public class StripePaymentServiceTests
             options.CustomerDetails.TaxExempt == StripeConstants.TaxExempt.Reverse
         ));
     }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_WithCustomerDiscount_ReturnsDiscountFromCustomer(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange
+        subscriber.Gateway = GatewayType.Stripe;
+        subscriber.GatewayCustomerId = "cus_test123";
+        subscriber.GatewaySubscriptionId = "sub_test123";
+
+        var customerDiscount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = StripeConstants.CouponIDs.Milestone2SubscriptionDiscount,
+                PercentOff = 20m,
+                AmountOff = 1400
+            },
+            End = null
+        };
+
+        var subscription = new Subscription
+        {
+            Id = "sub_test123",
+            Status = "active",
+            CollectionMethod = "charge_automatically",
+            Customer = new Customer
+            {
+                Discount = customerDiscount
+            },
+            Discounts = new List<Discount>(), // Empty list
+            Items = new StripeList<SubscriptionItem> { Data = [] }
+        };
+
+        sutProvider.GetDependency<IStripeAdapter>()
+            .SubscriptionGetAsync(
+                subscriber.GatewaySubscriptionId,
+                Arg.Any<SubscriptionGetOptions>())
+            .Returns(subscription);
+
+        // Act
+        var result = await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert
+        Assert.NotNull(result.CustomerDiscount);
+        Assert.Equal(StripeConstants.CouponIDs.Milestone2SubscriptionDiscount, result.CustomerDiscount.Id);
+        Assert.Equal(20m, result.CustomerDiscount.PercentOff);
+        Assert.Equal(14.00m, result.CustomerDiscount.AmountOff); // Converted from cents
+    }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_WithoutCustomerDiscount_FallsBackToSubscriptionDiscounts(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange
+        subscriber.Gateway = GatewayType.Stripe;
+        subscriber.GatewayCustomerId = "cus_test123";
+        subscriber.GatewaySubscriptionId = "sub_test123";
+
+        var subscriptionDiscount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = StripeConstants.CouponIDs.Milestone2SubscriptionDiscount,
+                PercentOff = 15m,
+                AmountOff = null
+            },
+            End = null
+        };
+
+        var subscription = new Subscription
+        {
+            Id = "sub_test123",
+            Status = "active",
+            CollectionMethod = "charge_automatically",
+            Customer = new Customer
+            {
+                Discount = null // No customer discount
+            },
+            Discounts = new List<Discount> { subscriptionDiscount },
+            Items = new StripeList<SubscriptionItem> { Data = [] }
+        };
+
+        sutProvider.GetDependency<IStripeAdapter>()
+            .SubscriptionGetAsync(
+                subscriber.GatewaySubscriptionId,
+                Arg.Any<SubscriptionGetOptions>())
+            .Returns(subscription);
+
+        // Act
+        var result = await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert - Should use subscription discount as fallback
+        Assert.NotNull(result.CustomerDiscount);
+        Assert.Equal(StripeConstants.CouponIDs.Milestone2SubscriptionDiscount, result.CustomerDiscount.Id);
+        Assert.Equal(15m, result.CustomerDiscount.PercentOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_WithBothDiscounts_PrefersCustomerDiscount(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange
+        subscriber.Gateway = GatewayType.Stripe;
+        subscriber.GatewayCustomerId = "cus_test123";
+        subscriber.GatewaySubscriptionId = "sub_test123";
+
+        var customerDiscount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = StripeConstants.CouponIDs.Milestone2SubscriptionDiscount,
+                PercentOff = 25m
+            },
+            End = null
+        };
+
+        var subscriptionDiscount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = "different-coupon-id",
+                PercentOff = 10m
+            },
+            End = null
+        };
+
+        var subscription = new Subscription
+        {
+            Id = "sub_test123",
+            Status = "active",
+            CollectionMethod = "charge_automatically",
+            Customer = new Customer
+            {
+                Discount = customerDiscount // Should prefer this
+            },
+            Discounts = new List<Discount> { subscriptionDiscount },
+            Items = new StripeList<SubscriptionItem> { Data = [] }
+        };
+
+        sutProvider.GetDependency<IStripeAdapter>()
+            .SubscriptionGetAsync(
+                subscriber.GatewaySubscriptionId,
+                Arg.Any<SubscriptionGetOptions>())
+            .Returns(subscription);
+
+        // Act
+        var result = await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert - Should prefer customer discount over subscription discount
+        Assert.NotNull(result.CustomerDiscount);
+        Assert.Equal(StripeConstants.CouponIDs.Milestone2SubscriptionDiscount, result.CustomerDiscount.Id);
+        Assert.Equal(25m, result.CustomerDiscount.PercentOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_WithNoDiscounts_ReturnsNullDiscount(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange
+        subscriber.Gateway = GatewayType.Stripe;
+        subscriber.GatewayCustomerId = "cus_test123";
+        subscriber.GatewaySubscriptionId = "sub_test123";
+
+        var subscription = new Subscription
+        {
+            Id = "sub_test123",
+            Status = "active",
+            CollectionMethod = "charge_automatically",
+            Customer = new Customer
+            {
+                Discount = null
+            },
+            Discounts = new List<Discount>(), // Empty list, no discounts
+            Items = new StripeList<SubscriptionItem> { Data = [] }
+        };
+
+        sutProvider.GetDependency<IStripeAdapter>()
+            .SubscriptionGetAsync(
+                subscriber.GatewaySubscriptionId,
+                Arg.Any<SubscriptionGetOptions>())
+            .Returns(subscription);
+
+        // Act
+        var result = await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert
+        Assert.Null(result.CustomerDiscount);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_WithMultipleSubscriptionDiscounts_SelectsFirstDiscount(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange - Multiple subscription-level discounts, no customer discount
+        subscriber.Gateway = GatewayType.Stripe;
+        subscriber.GatewayCustomerId = "cus_test123";
+        subscriber.GatewaySubscriptionId = "sub_test123";
+
+        var firstDiscount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = "coupon-10-percent",
+                PercentOff = 10m
+            },
+            End = null
+        };
+
+        var secondDiscount = new Discount
+        {
+            Coupon = new Coupon
+            {
+                Id = "coupon-20-percent",
+                PercentOff = 20m
+            },
+            End = null
+        };
+
+        var subscription = new Subscription
+        {
+            Id = "sub_test123",
+            Status = "active",
+            CollectionMethod = "charge_automatically",
+            Customer = new Customer
+            {
+                Discount = null // No customer discount
+            },
+            // Multiple subscription discounts - FirstOrDefault() should select the first one
+            Discounts = new List<Discount> { firstDiscount, secondDiscount },
+            Items = new StripeList<SubscriptionItem> { Data = [] }
+        };
+
+        sutProvider.GetDependency<IStripeAdapter>()
+            .SubscriptionGetAsync(
+                subscriber.GatewaySubscriptionId,
+                Arg.Any<SubscriptionGetOptions>())
+            .Returns(subscription);
+
+        // Act
+        var result = await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert - Should select the first discount from the list (FirstOrDefault() behavior)
+        Assert.NotNull(result.CustomerDiscount);
+        Assert.Equal("coupon-10-percent", result.CustomerDiscount.Id);
+        Assert.Equal(10m, result.CustomerDiscount.PercentOff);
+        // Verify the second discount was not selected
+        Assert.NotEqual("coupon-20-percent", result.CustomerDiscount.Id);
+        Assert.NotEqual(20m, result.CustomerDiscount.PercentOff);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_WithNullCustomer_HandlesGracefully(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange - Subscription with null Customer (defensive null check scenario)
+        subscriber.Gateway = GatewayType.Stripe;
+        subscriber.GatewayCustomerId = "cus_test123";
+        subscriber.GatewaySubscriptionId = "sub_test123";
+
+        var subscription = new Subscription
+        {
+            Id = "sub_test123",
+            Status = "active",
+            CollectionMethod = "charge_automatically",
+            Customer = null, // Customer not expanded or null
+            Discounts = new List<Discount>(), // Empty discounts
+            Items = new StripeList<SubscriptionItem> { Data = [] }
+        };
+
+        sutProvider.GetDependency<IStripeAdapter>()
+            .SubscriptionGetAsync(
+                subscriber.GatewaySubscriptionId,
+                Arg.Any<SubscriptionGetOptions>())
+            .Returns(subscription);
+
+        // Act
+        var result = await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert - Should handle null Customer gracefully without throwing NullReferenceException
+        Assert.Null(result.CustomerDiscount);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_WithNullDiscounts_HandlesGracefully(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange - Subscription with null Discounts (defensive null check scenario)
+        subscriber.Gateway = GatewayType.Stripe;
+        subscriber.GatewayCustomerId = "cus_test123";
+        subscriber.GatewaySubscriptionId = "sub_test123";
+
+        var subscription = new Subscription
+        {
+            Id = "sub_test123",
+            Status = "active",
+            CollectionMethod = "charge_automatically",
+            Customer = new Customer
+            {
+                Discount = null // No customer discount
+            },
+            Discounts = null, // Discounts not expanded or null
+            Items = new StripeList<SubscriptionItem> { Data = [] }
+        };
+
+        sutProvider.GetDependency<IStripeAdapter>()
+            .SubscriptionGetAsync(
+                subscriber.GatewaySubscriptionId,
+                Arg.Any<SubscriptionGetOptions>())
+            .Returns(subscription);
+
+        // Act
+        var result = await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert - Should handle null Discounts gracefully without throwing NullReferenceException
+        Assert.Null(result.CustomerDiscount);
+    }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_VerifiesCorrectExpandOptions(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange
+        subscriber.Gateway = GatewayType.Stripe;
+        subscriber.GatewayCustomerId = "cus_test123";
+        subscriber.GatewaySubscriptionId = "sub_test123";
+
+        var subscription = new Subscription
+        {
+            Id = "sub_test123",
+            Status = "active",
+            CollectionMethod = "charge_automatically",
+            Customer = new Customer { Discount = null },
+            Discounts = new List<Discount>(), // Empty list
+            Items = new StripeList<SubscriptionItem> { Data = [] }
+        };
+
+        var stripeAdapter = sutProvider.GetDependency<IStripeAdapter>();
+        stripeAdapter
+            .SubscriptionGetAsync(
+                Arg.Any<string>(),
+                Arg.Any<SubscriptionGetOptions>())
+            .Returns(subscription);
+
+        // Act
+        await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert - Verify expand options are correct
+        await stripeAdapter.Received(1).SubscriptionGetAsync(
+            subscriber.GatewaySubscriptionId,
+            Arg.Is<SubscriptionGetOptions>(o =>
+                o.Expand.Contains("customer.discount.coupon.applies_to") &&
+                o.Expand.Contains("discounts.coupon.applies_to") &&
+                o.Expand.Contains("test_clock")));
+    }
+
+    [Theory]
+    [BitAutoData]
+    public async Task GetSubscriptionAsync_WithEmptyGatewaySubscriptionId_ReturnsEmptySubscriptionInfo(
+        SutProvider<StripePaymentService> sutProvider,
+        User subscriber)
+    {
+        // Arrange
+        subscriber.GatewaySubscriptionId = null;
+
+        // Act
+        var result = await sutProvider.Sut.GetSubscriptionAsync(subscriber);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Null(result.Subscription);
+        Assert.Null(result.CustomerDiscount);
+        Assert.Null(result.UpcomingInvoice);
+
+        // Verify no Stripe API calls were made
+        await sutProvider.GetDependency<IStripeAdapter>()
+            .DidNotReceive()
+            .SubscriptionGetAsync(Arg.Any<string>(), Arg.Any<SubscriptionGetOptions>());
+    }
 }