test: improve assert messages in stream test

In test-stream-pipe-await-train-manual-resume, include unexpected value
in error messages.
PR-URL: #16884
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: katie-roberts

test/parallel/test-stream-pipe-await-drain-manual-resume.js

@@ -30,11 +30,13 @@ readable.once('pause', common.mustCall(() => {
 assert.strictEqual(
 readable._readableState.awaitDrain,
 1,
-'awaitDrain doesn\'t increase'
+'Expected awaitDrain to equal 1 but instead got '+
+`${readable._readableState.awaitDrain}`
 );
 // First pause, resume manually. The next write() to writable will still
 // return false, because chunks are still being buffered, so it will increase
 // the awaitDrain counter again.
+
 process.nextTick(common.mustCall(()=>{
 readable.resume();
 }));
@@ -43,7 +45,8 @@ readable.once('pause', common.mustCall(() => {
 assert.strictEqual(
 readable._readableState.awaitDrain,
 1,
-'.resume() does not reset counter'
+'.resume() should not reset the counter but instead got '+
+`${readable._readableState.awaitDrain}`
 );
 // Second pause, handle all chunks from now on. Once all callbacks that
 // are currently queued up are handled, the awaitDrain drain counter should
@@ -64,7 +67,8 @@ writable.on('finish', common.mustCall(() => {
 assert.strictEqual(
 readable._readableState.awaitDrain,
 0,
-'awaitDrain not 0 after all chunks are written'
+'awaitDrain should equal 0 after all chunks are written but instead got'+
+`${readable._readableState.awaitDrain}`
 );
 // Everything okay, all chunks were written.
 }));