tests/run-multitests.py: Improve error handling for communication error.

Fixes fatal crash if serial port access returns an error (for example: port
is native USB-CDC and the host hard faults during the test run). Instead of
crashing, have the runner mark this as a test run error and continue.

It's not certain the next test will run successfully, but this provides the
context of output showing what was happening when the communication error
occurred. Without this change, that output is lost when the fatal exception
terminates the runner process.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

Author: projectgus

tests/run-multitests.py

@@ -276,19 +276,22 @@ def stop(self):
     def readline(self):
         if self.finished:
             return None, None
-        if self.pyb.serial.inWaiting() == 0:
-            return None, None
-        out = self.pyb.read_until(1, (b"\r\n", b"\x04"))
-        if out.endswith(b"\x04"):
-            self.finished = True
-            out = out[:-1]
-            err = decode(self.pyb.read_until(1, b"\x04"))
-            err = err[:-1]
-            if not out and not err:
+        try:
+            if self.pyb.serial.inWaiting() == 0:
                 return None, None
-        else:
-            err = None
-        return decode(out.rstrip()), err
+            out = self.pyb.read_until(1, (b"\r\n", b"\x04"))
+            if out.endswith(b"\x04"):
+                self.finished = True
+                out = out[:-1]
+                err = decode(self.pyb.read_until(1, b"\x04"))
+                err = err[:-1]
+                if not out and not err:
+                    return None, None
+            else:
+                err = None
+            return decode(out.rstrip()), err
+        except OSError as e:
+            return None, "Failed to read from instance: {}".format(e)
 
     def write(self, data):
         self.pyb.serial.write(data)
@@ -434,7 +437,10 @@ def run_test_on_instances(test_file, num_instances, instances):
 
     # Stop all instances
     for idx in range(num_instances):
-        instances[idx].stop()
+        try:
+            instances[idx].stop()
+        except OSError as e:
+            output[idx].append("Runner failed to stop instance: {}".format(e))
 
     output_str = ""
     for idx, lines in enumerate(output):