crypto: fix error in deprecation message

The deprecation message for `crypto.Credentials` says to use
`tls.createSecureContext` but the correct property to use is
`tls.SecureContext()`.

Fix the deprecation message and add a test that checks the mappings of
deprecated properties and their warning messages.

PR-URL: https://github.com/nodejs/node/pull/6344
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/crypto.js

@@ -671,4 +671,4 @@ exports.__defineGetter__('createCredentials',
 exports.__defineGetter__('Credentials', internalUtil.deprecate(function() {
   return require('tls').SecureContext;
 }, 'crypto.Credentials is deprecated. ' +
-   'Use tls.createSecureContext instead.'));
+   'Use tls.SecureContext instead.'));

test/parallel/test-crypto-deprecated.js

@@ -0,0 +1,31 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+if (!common.hasCrypto) {
+  console.log('1..0 # Skipped: missing crypto');
+  return;
+}
+const crypto = require('crypto');
+const tls = require('tls');
+
+process.on('warning', common.mustCall((warning) => {
+  assert.strictEqual(warning.name, 'DeprecationWarning');
+  assert.notStrictEqual(expected.indexOf(warning.message), -1,
+                        `unexpected error message: "${warning.message}"`);
+  // Remove a warning message after it is seen so that we guarantee that we get
+  // each message only once.
+  expected.splice(expected.indexOf(warning.message), 1);
+}, 2));
+
+var expected = [
+  'crypto.Credentials is deprecated. Use tls.SecureContext instead.',
+  'crypto.createCredentials is deprecated. Use tls.createSecureContext instead.'
+];
+
+// Accessing the deprecated function is enough to trigger the warning event.
+// It does not need to be called. So the assert serves the purpose of both
+// triggering the warning event and confirming that the deprected function is
+// mapped to the correct non-deprecated function.
+assert.strictEqual(crypto.Credentials, tls.SecureContext);
+assert.strictEqual(crypto.createCredentials, tls.createSecureContext);