tests: Add tests for _thread module.

Includes functionality and stress tests.

tests/thread/thread_lock3.py

@@ -0,0 +1,27 @@
+# test thread coordination using a lock object
+#
+# MIT license; Copyright (c) 2016 Damien P. George on behalf of Pycom Ltd
+
+import _thread
+
+lock = _thread.allocate_lock()
+n_thread = 10
+n_finished = 0
+
+def thread_entry(idx):
+    global n_finished
+    while True:
+        with lock:
+            if n_finished == idx:
+                break
+    print('my turn:', idx)
+    with lock:
+        n_finished += 1
+
+# spawn threads
+for i in range(n_thread):
+    _thread.start_new_thread(thread_entry, (i,))
+
+# busy wait for threads to finish
+while n_finished < n_thread:
+    pass