simpleRestJson: add protocol tests for default body behavior

modules/protocol-tests/resources/META-INF/smithy/HttpPayloadWithDefault.smithy

@@ -0,0 +1,56 @@
+$version: "2"
+
+namespace alloy.test
+
+use alloy#simpleRestJson
+use smithy.test#httpRequestTests
+use smithy.test#httpResponseTests
+
+apply HttpPayloadWithDefault @httpRequestTests([{
+    id: "SimpleRestJsonSomeHttpPayloadWithDefault"
+    documentation: "Pass JSON string value as is if payload provided"
+    protocol: simpleRestJson
+    method: "PUT"
+    uri: "/httpPayloadWithDefault"
+    body: "\"custom value\""
+    headers: {
+        "Content-Type": "application/json"
+    }
+    requireHeaders: ["Content-Length"]
+    params: {
+        body: "custom value"
+    }
+    bodyMediaType: "application/json"
+}, {
+    id: "SimpleRestJsonNoneHttpPayloadWithDefault"
+    documentation: "Use default value when there is no payload"
+    protocol: simpleRestJson
+    method: "PUT"
+    uri: "/httpPayloadWithDefault"
+    params: {
+        body: "default value"
+    }
+}])
+
+apply HttpPayloadWithDefault @httpResponseTests([{
+    id: "SimpleRestJsonSomeHttpPayloadWithDefault"
+    documentation: "Pass JSON string value as is if payload provided"
+    protocol: simpleRestJson
+    code: 200
+    body: "\"custom value\""
+    bodyMediaType: "application/json"
+    headers: {
+        "Content-Type": "application/json"
+    }
+    params: {
+        body: "custom value"
+    }
+}, {
+    id: "SimpleRestJsonNoneHttpPayloadWithDefault"
+    documentation: "Use default value when there is no payload"
+    protocol: simpleRestJson
+    code: 200
+    params: {
+        body: "default value"
+    }
+}])

modules/protocol-tests/resources/META-INF/smithy/Pizza.smithy

@@ -9,7 +9,7 @@ use alloy#simpleRestJson
 service PizzaAdminService {
     version: "1.0.0",
     errors: [GenericServerError, GenericClientError],
-    operations: [AddMenuItem, GetMenu, Version, Health, HeaderEndpoint, RoundTrip, GetEnum, GetIntEnum, CustomCode]
+    operations: [AddMenuItem, GetMenu, Version, Health, HeaderEndpoint, RoundTrip, GetEnum, GetIntEnum, CustomCode, HttpPayloadWithDefault]
 }
 
 @http(method: "POST", uri: "/restaurant/{restaurant}/menu/item", code: 201)
@@ -302,4 +302,17 @@ structure CustomCodeInput {
 structure CustomCodeOutput {
     @httpResponseCode
     code: Integer
-}
+}
+
+@idempotent
+@http(uri: "/httpPayloadWithDefault", method: "PUT")
+operation HttpPayloadWithDefault {
+    input: HttpPayloadWithDefaultInputOutput,
+    output: HttpPayloadWithDefaultInputOutput
+}
+
+structure HttpPayloadWithDefaultInputOutput {
+    @httpPayload
+    @default("default value")
+    body: String,
+}

modules/protocol-tests/resources/META-INF/smithy/manifest

@@ -8,4 +8,5 @@ Health.smithy
 Pizza.smithy
 RoundTrip.smithy
 Version.smithy
-test-config.json
+HttpPayloadWithDefault.smithy
+test-config.json