test: implement common.log

Enable logs by setting the `DEBUG` environment variable, or by passing
`--log` or `-l` to the script.

Could probably be enhanced to send logs somewhere other than stdout, but
I haven't found a need for that yet.

Fixes: nodejs#9314

test/common/README.md

@@ -271,6 +271,11 @@ IP of `localhost`.
 
 Array of IPV6 representations for `localhost`.
 
+### log([data])
+* return [<Function>]
+
+Configurable console logging.
+
 ### mustCall([fn][, exact])
 * `fn` [<Function>] default = () => {}
 * `exact` [<number>] default = 1

test/common/index.js

@@ -68,6 +68,14 @@ exports.rootDir = exports.isWindows ? 'c:\\' : '/';
 
 exports.buildType = process.config.target_defaults.default_configuration;
 
+if (process.env.DEBUG) {
+  const { Console } = require('console');
+  const logger = new Console(process.stdout, process.stderr);
+  exports.log = logger.log;
+} else {
+  exports.log = () => {};
+}
+
 // If env var is set then enable async_hook hooks for all tests.
 if (process.env.NODE_TEST_WITH_ASYNC_HOOKS) {
   const destroydIdsList = {};

test/parallel/test-buffer-new.js

@@ -2,6 +2,8 @@
 
 const common = require('../common');
 
+common.log('foo');
+
 common.expectsError(() => new Buffer(42, 'utf8'), {
   code: 'ERR_INVALID_ARG_TYPE',
   type: TypeError,

test/parallel/test-stream2-readable-empty-buffer-no-eof.js

@@ -20,7 +20,7 @@
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 'use strict';
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 
 const Readable = require('stream').Readable;
@@ -85,7 +85,7 @@ function test1() {
 
   process.on('exit', function() {
     assert.deepStrictEqual(results, [ 'xxxxx', 'xxxxx', 'EOF' ]);
-    console.log('ok');
+    common.log('ok');
   });
 }
 
@@ -113,6 +113,6 @@ function test2() {
 
   process.on('exit', function() {
     assert.deepStrictEqual(results, [ 'eHh4', 'eHg=', 'EOF' ]);
-    console.log('ok');
+    common.log('ok');
   });
 }

tools/test.py

@@ -1350,6 +1350,8 @@ def BuildOptions():
   result = optparse.OptionParser()
   result.add_option("-m", "--mode", help="The test modes in which to run (comma-separated)",
       default='release')
+  result.add_option("-l", "--log", help="Enable logging using common.log",
+      default=False, action="store_true")
   result.add_option("-v", "--verbose", help="Verbose output",
       default=False, action="store_true")
   result.add_option('--logfile', dest='logfile',
@@ -1694,6 +1696,9 @@ def Main():
     for rule in globally_unused_rules:
       print "Rule for '%s' was not used." % '/'.join([str(s) for s in rule.path])
 
+  if options.log:
+    os.environ['DEBUG'] = 'true'
+
   tempdir = os.environ.get('NODE_TEST_DIR') or options.temp_dir
   if tempdir:
     os.environ['NODE_TEST_DIR'] = tempdir