Validate resolvedHost from httpRequestTests (#1300)

Author: trivikr

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

@@ -448,6 +448,7 @@ private void writeHttpRequestAssertions(HttpRequestTestCase testCase) {
 
         writeHttpHeaderAssertions(testCase);
         writeHttpQueryAssertions(testCase);
+        writeHttpHostAssertion(testCase);
         testCase.getBody().ifPresent(body -> {
             writeHttpBodyAssertions(body, testCase.getBodyMediaType().orElse("UNKNOWN"), true);
         });
@@ -521,6 +522,14 @@ private void writeHttpHeaderAssertions(HttpMessageTestCase testCase) {
         writer.write("");
     }
 
+    private void writeHttpHostAssertion(HttpRequestTestCase testCase) {
+        testCase.getResolvedHost().ifPresent(resolvedHost -> {
+            writer.write("expect(r.headers[\"host\"]).toBeDefined();");
+            writer.write("expect(r.headers[\"host\"]).toBe($S);", resolvedHost);
+            writer.write("");
+        });
+    }
+
     private void writeHttpBodyAssertions(String body, String mediaType, boolean isClientTest) {
         // If we expect an empty body, expect it to be falsy.
         if (body.isEmpty()) {