test: improve coverage of stream.Readable

PR-URL: #38702
Refs: https://coverage.nodejs.org/coverage-0996eb71edbd47d9/lib/internal/streams/readable.js.html#L401
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

test/parallel/test-streams-highwatermark.js

@@ -59,3 +59,16 @@ const { inspect } = require('util');
   readable._read = common.mustCall();
   readable.read(0);
 }
+
+{
+  // Parse size as decimal integer
+  ['1', '1.0', 1].forEach((size) => {
+    const readable = new stream.Readable({
+      read: common.mustCall(),
+      highWaterMark: 0,
+    });
+    readable.read(size);
+
+    assert.strictEqual(readable._readableState.highWaterMark, Number(size));
+  });
+}