test: improve coverage of the buffer module

Add tests for untested branches and statements.
Also convert some lines to const.

PR-URL: #8552
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

test/parallel/test-buffer-alloc.js

@@ -26,6 +26,14 @@ assert.strictEqual(512, c.length);
 const d = Buffer.from([]);
 assert.strictEqual(0, d.length);
 
+// Test offset properties
+{
+  const b = Buffer.alloc(128);
+  assert.strictEqual(128, b.length);
+  assert.strictEqual(0, b.byteOffset);
+  assert.strictEqual(0, b.offset);
+}
+
 // Test creating a Buffer from a Uint32Array
 {
   const ui32 = new Uint32Array(4).fill(42);
@@ -49,6 +57,9 @@ assert.throws(() => b.toString('invalid'),
 // invalid encoding for Buffer.write
 assert.throws(() => b.write('test string', 0, 5, 'invalid'),
               /Unknown encoding: invalid/);
+// unsupported arguments for Buffer.write
+assert.throws(() => b.write('test', 'utf8', 0),
+              /is no longer supported/);
 
 
 // try to create 0-length buffers
@@ -706,6 +717,16 @@ assert.strictEqual('<Buffer 81 a3 66 6f 6f a3 62 61 72>', x.inspect());
   assert.strictEqual(buf[4], 0);
 }
 
+{
+  // test alloc with fill option
+  const buf = Buffer.alloc(5, '800A', 'hex');
+  assert.strictEqual(buf[0], 128);
+  assert.strictEqual(buf[1], 10);
+  assert.strictEqual(buf[2], 128);
+  assert.strictEqual(buf[3], 10);
+  assert.strictEqual(buf[4], 128);
+}
+
 
 // Check for fractional length args, junk length args, etc.
 // https://github.com/joyent/node/issues/1758

test/parallel/test-buffer-compare-offset.js

@@ -15,7 +15,7 @@ assert.strictEqual(-1, a.compare(b, '0'));
 // Equivalent to a.compare(b).
 assert.strictEqual(-1, a.compare(b, 0, undefined, 0));
 
-// Zero-length targer, return 1
+// Zero-length target, return 1
 assert.strictEqual(1, a.compare(b, 0, 0, 0));
 assert.strictEqual(1, a.compare(b, '0', '0', '0'));
 
@@ -25,6 +25,10 @@ assert.strictEqual(1, a.compare(b, 6, 10));
 // Zero-length source, return -1
 assert.strictEqual(-1, a.compare(b, 6, 10, 0, 0));
 
+// Zero-length source and target, return 0
+assert.strictEqual(0, a.compare(b, 0, 0, 0, 0));
+assert.strictEqual(0, a.compare(b, 1, 1, 2, 2));
+
 // Equivalent to Buffer.compare(a.slice(4), b.slice(0, 5))
 assert.strictEqual(1, a.compare(b, 0, 5, 4));
 

test/parallel/test-buffer-indexof.js

@@ -1,15 +1,15 @@
 'use strict';
 require('../common');
-var assert = require('assert');
+const assert = require('assert');
 
-var Buffer = require('buffer').Buffer;
+const Buffer = require('buffer').Buffer;
 
-var b = Buffer.from('abcdef');
-var buf_a = Buffer.from('a');
-var buf_bc = Buffer.from('bc');
-var buf_f = Buffer.from('f');
-var buf_z = Buffer.from('z');
-var buf_empty = Buffer.from('');
+const b = Buffer.from('abcdef');
+const buf_a = Buffer.from('a');
+const buf_bc = Buffer.from('bc');
+const buf_f = Buffer.from('f');
+const buf_z = Buffer.from('z');
+const buf_empty = Buffer.from('');
 
 assert.equal(b.indexOf('a'), 0);
 assert.equal(b.indexOf('a', 1), -1);
@@ -78,6 +78,12 @@ assert.equal(b.indexOf(Buffer.from('f'), 6), -1);
 
 assert.equal(Buffer.from('ff').indexOf(Buffer.from('f'), 1, 'ucs2'), -1);
 
+// test invalid and uppercase encoding
+assert.strictEqual(b.indexOf('b', 'utf8'), 1);
+assert.strictEqual(b.indexOf('b', 'UTF8'), 1);
+assert.strictEqual(b.indexOf('62', 'HEX'), 1);
+assert.throws(() => b.indexOf('bad', 'enc'), /Unknown encoding: enc/);
+
 // test hex encoding
 assert.strictEqual(
   Buffer.from(b.toString('hex'), 'hex')

test/parallel/test-buffer-new.js

@@ -0,0 +1,7 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const Buffer = require('buffer').Buffer;
+
+assert.throws(() => new Buffer(42, 'utf8'), /first argument must be a string/);