test: expand test coverage of fs.js

* test calling truncateSync() passing a file descriptor
* test calling truncate() passing undefined as the 2nd argument

Refs: https://coverage.nodejs.org/coverage-8ab561b2432bdae3/root/fs.js.html
      (line 673 and 692)

PR-URL: https://github.com/nodejs/node/pull/10972
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/test/parallel/test-fs-truncate.js b/test/parallel/test-fs-truncate.js
index 80c938b8d4..57d706bddb 100644
--- a/test/parallel/test-fs-truncate.js
+++ b/test/parallel/test-fs-truncate.js
@@ -146,3 +146,14 @@ function testFtruncate(cb) {
     assert(fs.readFileSync(file4).equals(Buffer.from('Hi\u0000\u0000')));
   }));
 }
+
+{
+  const file5 = path.resolve(tmp, 'truncate-file-5.txt');
+  fs.writeFileSync(file5, 'Hi');
+  const fd = fs.openSync(file5, 'r+');
+  process.on('exit', () => fs.closeSync(fd));
+  fs.ftruncate(fd, undefined, common.mustCall(function(err) {
+    assert.ifError(err);
+    assert(fs.readFileSync(file5).equals(Buffer.from('')));
+  }));
+}