Add query parameter list serialization test for CSV format

.chronus/changes/query-list-parameter-2025-12-17-23-13-48.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/http-specs"
+---
+
+Add test for query parameter with list/array type to verify CSV serialization

packages/http-specs/spec-summary.md

@@ -1354,6 +1354,14 @@ Second request path:
 
 Expect to handle a constant value for query and mock api returns nothing
 
+### Parameters_Query_QueryList_post
+
+- Endpoint: `post /parameters/query/list`
+
+Expect to handle a list of values for query parameter.
+The list should be serialized as CSV (comma-separated values).
+Pass array ["a", "b", "c"] and expect it to be serialized as "a,b,c".
+
 ### Parameters_Spread_Alias_spreadAsRequestBody
 
 - Endpoint: `put /parameters/spread/alias/request-body`

packages/http-specs/specs/parameters/query/main.tsp

@@ -20,3 +20,20 @@ interface Constant {
     queryParam: "constantValue",
   ): void;
 }
+
+@doc("List query parameter verification")
+@route("/list")
+interface QueryList {
+  /** send list query parameter */
+  @scenario
+  @scenarioDoc("""
+    Expect to handle a list of values for query parameter.
+    The list should be serialized as CSV (comma-separated values).
+    Pass array ["a", "b", "c"] and expect it to be serialized as "a,b,c".
+    """)
+  @post
+  post(
+    @query
+    listParameter: string[],
+  ): void;
+}

packages/http-specs/specs/parameters/query/mockapi.ts

@@ -13,3 +13,15 @@ Scenarios.Parameters_Query_Constant_post = passOnSuccess({
   },
   kind: "MockApiDefinition",
 });
+
+Scenarios.Parameters_Query_QueryList_post = passOnSuccess({
+  uri: "/parameters/query/list",
+  method: `post`,
+  request: {
+    query: { listParameter: "a,b,c" },
+  },
+  response: {
+    status: 204,
+  },
+  kind: "MockApiDefinition",
+});