handle unset unions

Author: kuhe

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/HttpProtocolTestGenerator.java

@@ -545,9 +545,11 @@ private void writeHttpHostAssertion(HttpRequestTestCase testCase) {
     }
 
     private void writeHttpBodyAssertions(String body, String mediaType, boolean isClientTest) {
-        // If we expect an empty body, expect it to be falsy.
         if (body.isEmpty()) {
-            writer.write("expect(r.body).toBeFalsy();");
+            // If we expect an empty body, expect it to be falsy.
+            // Or, for JSON an empty object represents an empty body.
+            // mediaType is often UNKNOWN here.
+            writer.write("expect(r.body && Object.keys(r.body).length).toBeFalsy();");
             return;
         }
 

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/integration/HttpBindingProtocolGenerator.java

@@ -2466,16 +2466,29 @@ private HttpBinding readPayload(
             // If payload is a Union, then we need to parse the string into JavaScript object.
             importUnionDeserializer(writer);
             writer.write("const data: Record<string, any> | undefined "
-                    + "= __expectUnion(await parseBody(output.body, context));");
+                    + "= await parseBody(output.body, context);");
         } else if (target instanceof StringShape || target instanceof DocumentShape) {
             // If payload is String or Document, we need to collect body and convert binary to string.
             writer.write("const data: any = await collectBodyString(output.body, context);");
         } else {
             throw new CodegenException(String.format("Unexpected shape type bound to payload: `%s`",
                     target.getType()));
         }
-        writer.write("contents.$L = $L;", binding.getMemberName(), getOutputValue(context,
+
+        if (target instanceof UnionShape) {
+            writer.openBlock(
+                "if (Object.keys(data ?? {}).length) {",
+                "}",
+                () -> {
+                    writer.write("contents.$L = __expectUnion($L);", binding.getMemberName(), getOutputValue(context,
+                        Location.PAYLOAD, "data", binding.getMember(), target));
+                }
+            );
+        } else {
+            writer.write("contents.$L = $L;", binding.getMemberName(), getOutputValue(context,
                 Location.PAYLOAD, "data", binding.getMember(), target));
+        }
+
         return binding;
     }