tests: Add tests using "file" argument in print and sys.print_exception.

tests/io/builtin_print_file.py

@@ -0,0 +1,17 @@
+# test builtin print function, using file= argument
+
+import sys
+
+try:
+    sys.stdout
+except AttributeError:
+    print('SKIP')
+    raise SystemExit
+
+print(file=sys.stdout)
+print('test', file=sys.stdout)
+
+try:
+    print(file=1)
+except (AttributeError, OSError): # CPython and uPy differ in error message
+    print('Error')

tests/misc/print_exception.py

@@ -56,3 +56,12 @@ try:
     f()
 except Exception as e:
     print_exc(e)
+
+# Test non-stream object passed as output object, only valid for uPy
+if hasattr(sys, 'print_exception'):
+    try:
+        sys.print_exception(Exception, 1)
+        had_exception = False
+    except OSError:
+        had_exception = True
+    assert had_exception