test: apply promises API to third appendFile test

Add tests for `fs.promises.appendFile()` to the third (of five) test case in `test-fs-access`. (First and second test cases already have promises API versions.) PR-URL: #21131 Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: Trivikram Kamat <[email protected]>

Author: Trott

test/parallel/test-fs-append-file.js

@@ -100,23 +100,37 @@ const throwNextTick = (e) =>{process.nextTick(() =>{throw e})};
 .catch(throwNextTick);
 }
 
-// test that appendFile accepts buffers
-constfilename3=join(tmpdir.path,'append3.txt');
-fs.writeFileSync(filename3,currentFileData);
+// test that appendFile accepts buffers (callback API)
+{
+constfilename=join(tmpdir.path,'append-buffer.txt');
+fs.writeFileSync(filename,currentFileData);
 
-constbuf=Buffer.from(s,'utf8');
+constbuf=Buffer.from(s,'utf8');
 
-fs.appendFile(filename3,buf,function(e){
-assert.ifError(e);
+fs.appendFile(filename,buf,common.mustCall((e)=>{
+assert.ifError(e);
 
-ncallbacks++;
+fs.readFile(filename,common.mustCall((e,buffer)=>{
+assert.ifError(e);
+assert.strictEqual(buf.length+currentFileData.length,buffer.length);
+}));
+}));
+}
 
-fs.readFile(filename3,function(e,buffer){
-assert.ifError(e);
-ncallbacks++;
-assert.strictEqual(buf.length+currentFileData.length,buffer.length);
-});
-});
+// test that appendFile accepts buffers (promises API)
+{
+constfilename=join(tmpdir.path,'append-buffer-promises.txt');
+fs.writeFileSync(filename,currentFileData);
+
+constbuf=Buffer.from(s,'utf8');
+
+fs.promises.appendFile(filename,buf)
+.then(common.mustCall(()=>fs.promises.readFile(filename)))
+.then((buffer)=>{
+assert.strictEqual(buf.length+currentFileData.length,buffer.length);
+})
+.catch(throwNextTick);
+}
 
 // test that appendFile accepts numbers.
 constfilename4=join(tmpdir.path,'append4.txt');
@@ -177,9 +191,8 @@ assert.throws(
 {code: 'ERR_INVALID_CALLBACK'});
 
 process.on('exit',function(){
-assert.strictEqual(ncallbacks,8);
+assert.strictEqual(ncallbacks,6);
 
-fs.unlinkSync(filename3);
 fs.unlinkSync(filename4);
 fs.unlinkSync(filename5);
 });