Fix duplicate expand values issue

src/Stripe.net/Services/_base/Service.cs

@@ -296,7 +296,16 @@ protected BaseOptions SetupOptions(BaseOptions options, bool isListMethod)
             }
 
             options = options ?? new BaseOptions();
-            options.AddRangeExpand(serviceExpansions);
+
+            if (options.Expand == null)
+            {
+                options.Expand = new List<string>();
+            }
+
+            // Compute the union instead of using `AddRangeExpand` to avoid adding duplicate
+            // values in the list, in case `SetupOptions` has already been called on this options
+            // instance.
+            options.Expand = options.Expand.Union(serviceExpansions).ToList();
 
             return options;
         }

src/StripeTests/Services/AutoPagingTest.cs

@@ -44,6 +44,7 @@ public void ListAutoPaging()
 
             // Call auto-paging method
             var service = new PageableService(this.StripeClient);
+            service.ExpandFoo = true;
             var options = new ListOptions
             {
                 Limit = 2,
@@ -66,7 +67,7 @@ public void ListAutoPaging()
                     ItExpr.Is<HttpRequestMessage>(m =>
                         m.Method == HttpMethod.Get &&
                         m.RequestUri.AbsolutePath == "/v1/pageablemodels" &&
-                        m.RequestUri.Query == "?limit=2"),
+                        m.RequestUri.Query == "?limit=2&expand[0]=data.foo"),
                     ItExpr.IsAny<CancellationToken>());
 
             this.MockHttpClientFixture.MockHandler.Protected()
@@ -76,7 +77,7 @@ public void ListAutoPaging()
                     ItExpr.Is<HttpRequestMessage>(m =>
                         m.Method == HttpMethod.Get &&
                         m.RequestUri.AbsolutePath == "/v1/pageablemodels" &&
-                        m.RequestUri.Query == "?limit=2&starting_after=pm_124"),
+                        m.RequestUri.Query == "?limit=2&starting_after=pm_124&expand[0]=data.foo"),
                     ItExpr.IsAny<CancellationToken>());
 
             this.MockHttpClientFixture.MockHandler.Protected()
@@ -86,7 +87,7 @@ public void ListAutoPaging()
                     ItExpr.Is<HttpRequestMessage>(m =>
                         m.Method == HttpMethod.Get &&
                         m.RequestUri.AbsolutePath == "/v1/pageablemodels" &&
-                        m.RequestUri.Query == "?limit=2&starting_after=pm_126"),
+                        m.RequestUri.Query == "?limit=2&starting_after=pm_126&expand[0]=data.foo"),
                     ItExpr.IsAny<CancellationToken>());
         }
 
@@ -170,6 +171,8 @@ public PageableService(IStripeClient client)
             {
             }
 
+            public bool ExpandFoo { get; set; }
+
             public override string BasePath => "/v1/pageablemodels";
 
             public IEnumerable<PageableModel> ListAutoPaging(ListOptions options = null)

src/StripeTests/Services/_base/ServiceTest.cs

@@ -21,6 +21,7 @@ public void Get_ExpandProperties()
             service.ExpandMultiWordProperty = true;
             service.Get("foo");
 
+            Assert.Equal(2, client.LastOptions.Expand.Count);
             Assert.Contains("simple", client.LastOptions.Expand);
             Assert.Contains("multi_word_property", client.LastOptions.Expand);
         }
@@ -60,8 +61,18 @@ public void List_ExpandProperties()
 
             service.ExpandSimple = true;
             service.ExpandMultiWordProperty = true;
-            service.List();
+            var options = new ListOptions();
 
+            service.List(options);
+
+            Assert.Equal(2, client.LastOptions.Expand.Count);
+            Assert.Contains("data.simple", client.LastOptions.Expand);
+            Assert.Contains("data.multi_word_property", client.LastOptions.Expand);
+
+            // Do a second request to check that expand properties are not duplicated
+            service.List(options);
+
+            Assert.Equal(2, client.LastOptions.Expand.Count);
             Assert.Contains("data.simple", client.LastOptions.Expand);
             Assert.Contains("data.multi_word_property", client.LastOptions.Expand);
         }