LibTest: Fail if the top-level result of running a JS file is an error

Before putting `throw 1;` in a test file did not fail the file, and it
ignored the rest of the file. Now we check the resulting completion from
run and fail if that is an error.

Userland/Libraries/LibTest/JavaScriptTestRunner.h

@@ -373,6 +373,7 @@ inline JSFileResult TestRunner::run_file_test(String const& test_path)
     }
 
     auto file_script = parse_script(test_path, interpreter->realm());
+    JS::ThrowCompletionOr<JS::Value> top_level_result { JS::js_undefined() };
     if (file_script.is_error())
         return { test_path, file_script.error() };
     if (g_run_bytecode) {
@@ -383,11 +384,11 @@ inline JSFileResult TestRunner::run_file_test(String const& test_path)
             if (JS::Bytecode::g_dump_bytecode)
                 executable->dump();
             JS::Bytecode::Interpreter bytecode_interpreter(interpreter->realm());
-            (void)bytecode_interpreter.run(*executable);
+            top_level_result = bytecode_interpreter.run(*executable);
         }
     } else {
         g_vm->push_execution_context(global_execution_context);
-        (void)interpreter->run(file_script.value());
+        top_level_result = interpreter->run(file_script.value());
         g_vm->pop_execution_context();
     }
 
@@ -459,6 +460,46 @@ inline JSFileResult TestRunner::run_file_test(String const& test_path)
         file_result.suites.append(suite);
     });
 
+    if (top_level_result.is_error()) {
+        Test::Suite suite { test_path, "<top-level>" };
+        suite.most_severe_test_result = Result::Crashed;
+
+        Test::Case test_case { "<top-level>", Test::Result::Fail, "", 0 };
+        auto error = top_level_result.release_error().release_value().release_value();
+        if (error.is_object()) {
+            StringBuilder detail_builder;
+
+            auto& error_object = error.as_object();
+            auto name = error_object.get_without_side_effects(g_vm->names.name).value_or(JS::js_undefined());
+            auto message = error_object.get_without_side_effects(g_vm->names.message).value_or(JS::js_undefined());
+
+            if (name.is_accessor() || message.is_accessor()) {
+                detail_builder.append(error.to_string_without_side_effects());
+            } else {
+                detail_builder.append(name.to_string_without_side_effects());
+                detail_builder.append(": "sv);
+                detail_builder.append(message.to_string_without_side_effects());
+            }
+
+            if (is<JS::Error>(error_object)) {
+                auto& error_as_error = static_cast<JS::Error&>(error_object);
+                detail_builder.append('\n');
+                detail_builder.append(error_as_error.stack_string());
+            }
+
+            test_case.details = detail_builder.to_string();
+        } else {
+            test_case.details = error.to_string_without_side_effects();
+        }
+
+        suite.tests.append(move(test_case));
+
+        file_result.suites.append(suite);
+
+        m_counts.suites_failed++;
+        file_result.most_severe_test_result = Test::Result::Fail;
+    }
+
     m_counts.files_total++;
 
     file_result.time_taken = get_time_in_ms() - start_time;