Test progress.total and improve docs

readme.md

@@ -810,7 +810,7 @@ Progress events for uploading (sending a request) and downloading (receiving a r
 }
 ```
 
-If it's not possible to retrieve the body size (can happen when streaming), `total` will be `undefined`.
+If the `content-length` header is missing, `total` will be `undefined`.
 
 ```js
 (async () => {

test/progress.ts

@@ -85,6 +85,7 @@ test('download progress - missing total size', withServer, async (t, server, got
 
 	await got('').on('downloadProgress', (event: Progress) => events.push(event));
 
+	t.is(events[0].total, undefined);
 	checkEvents(t, events);
 });
 
@@ -183,6 +184,7 @@ test('upload progress - stream with unknown body size', withServer, async (t, se
 		stream.pipeline(toReadableStream(file), request, () => {})
 	);
 
+	t.is(events[0].total, undefined);
 	checkEvents(t, events);
 });