tests/run-tests: Add --via-mpy option to run test from precompiled code.

With mpy-cross built, tests can now be run by first compiling them to .mpy
files, and then executing the .mpy file.  Usage: ./run-tests --via-mpy

tests/run-tests

@@ -18,6 +18,9 @@ else:
     CPYTHON3 = os.getenv('MICROPY_CPYTHON3', 'python3')
     MICROPYTHON = os.getenv('MICROPY_MICROPYTHON', '../unix/micropython')
 
+# mpy-cross is only needed if --via-mpy command-line arg is passed
+MPYCROSS = os.getenv('MICROPY_MPYCROSS', '../mpy-cross/mpy-cross')
+
 # Set PYTHONIOENCODING so that CPython will use utf-8 on systems which set another encoding in the locale
 os.environ['PYTHONIOENCODING'] = 'utf-8'
 os.environ['MICROPYPATH'] = ''
@@ -105,15 +108,30 @@ def run_micropython(pyb, args, test_file):
                 return b'CRASH'
 
         else:
-            # a standard test
-            try:
-                cmdlist = [MICROPYTHON, '-X', 'emit=' + args.emit]
-                if args.heapsize is not None:
-                    cmdlist.extend(['-X', 'heapsize=' + args.heapsize])
+            # a standard test run on PC
+
+            # create system command
+            cmdlist = [MICROPYTHON, '-X', 'emit=' + args.emit]
+            if args.heapsize is not None:
+                cmdlist.extend(['-X', 'heapsize=' + args.heapsize])
+
+            # if running via .mpy, first compile the .py file
+            if args.via_mpy:
+                subprocess.check_output([MPYCROSS, '-mcache-lookup-bc', '-o', 'mpytest.mpy', test_file])
+                cmdlist.extend(['-m', 'mpytest'])
+            else:
                 cmdlist.append(test_file)
+
+            # run the actual test
+            try:
                 output_mupy = subprocess.check_output(cmdlist)
             except subprocess.CalledProcessError:
                 output_mupy = b'CRASH'
+
+            # clean up if we had an intermediate .mpy file
+            if args.via_mpy:
+                rm_f('mpytest.mpy')
+
     else:
         # run on pyboard
         import pyboard
@@ -360,6 +378,7 @@ def main():
     cmd_parser.add_argument('--write-exp', action='store_true', help='save .exp files to run tests w/o CPython')
     cmd_parser.add_argument('--emit', default='bytecode', help='MicroPython emitter to use (bytecode or native)')
     cmd_parser.add_argument('--heapsize', help='heapsize to use (use default if not specified)')
+    cmd_parser.add_argument('--via-mpy', action='store_true', help='compile .py files to .mpy first')
     cmd_parser.add_argument('files', nargs='*', help='input test files')
     args = cmd_parser.parse_args()