Allow instance reuse with differing toBuffer options (#1860)

test/unit/toBuffer.js

@@ -0,0 +1,19 @@
+'use strict';
+
+const assert = require('assert');
+
+const sharp = require('../../');
+const fixtures = require('../fixtures');
+
+describe('toBuffer', () => {
+  it('reusing same sharp object does not reset previously passed parameters to toBuffer', (done) => {
+    let image = sharp(fixtures.inputJpg);
+    image.toBuffer({ resolveWithObject: true }).then((obj) => {
+      image.toBuffer().then((buff) => {
+        assert.strict.equal(Buffer.isBuffer(buff), true);
+        assert.strict.equal(typeof obj, 'object');
+        done();
+      });
+    });
+  });
+});