lib: added test case for consumers.js and blob.js

Added test cases for the code changes.

Fixes: nodejs#39804
Refs: https://fetch.spec.whatwg.org/#body-mixin

Author: git-srinivas

test/parallel/test-blob.js

@@ -87,6 +87,15 @@ assert.throws(() => new Blob({}), {
   }));
 }
 
+{
+  const b = new Blob(['hello', Buffer.from('world\ud801')]);
+  assert.strictEqual(b.size, 13);
+  b.text().then(common.mustCall((text) => {
+    assert.strictEqual(text, 'helloworld\ufffd');
+    assert.strictEqual(text.length, 11);
+  }));
+}
+
 {
   const b = new Blob(
     [

test/parallel/test-stream-consumers.js

@@ -73,6 +73,18 @@ const kArrayBuffer =
   setTimeout(() => passthrough.end('there'), 10);
 }
 
+{
+  const passthrough = new PassThrough();
+
+  text(passthrough).then(common.mustCall(async (str) => {
+    assert.strictEqual(str.length, 11);
+    assert.deepStrictEqual(str, 'hellothere\ufffd');
+  }));
+
+  passthrough.write('hello');
+  setTimeout(() => passthrough.end('there\ud801'), 10);
+}
+
 {
   const passthrough = new PassThrough();