test: add test for exec() known issue

PR-URL: https://github.com/nodejs/node/pull/7375
Refs: https://github.com/nodejs/node/issues/7342
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

test/known_issues/test-child-process-exec-stdout-data-string.js

@@ -0,0 +1,16 @@
+'use strict';
+// Refs: https://github.com/nodejs/node/issues/7342
+const common = require('../common');
+const assert = require('assert');
+const exec = require('child_process').exec;
+
+const expectedCalls = 2;
+
+const cb = common.mustCall((data) => {
+  assert.strictEqual(typeof data, 'string');
+}, expectedCalls);
+
+const command = common.isWindows ? 'dir' : 'ls';
+exec(command).stdout.on('data', cb);
+
+exec('fhqwhgads').stderr.on('data', cb);