gh-116622: Android test script improvements (#124012)

* Set Android test script stdout to line-buffered
* Print warning logcat messages on stderr
* Add a -vv option to display high-volume messages which are rarely useful
* Documentation and comment improvements

Android/README.md

@@ -12,8 +12,12 @@ approachable user experience:
 
 ## Prerequisites
 
-Export the `ANDROID_HOME` environment variable to point at your Android SDK. If
-you don't already have the SDK, here's how to install it:
+First, make sure you have all the usual tools and libraries needed to build
+Python for your development machine.
+
+Second, you'll need an Android SDK. If you already have the SDK installed,
+export the `ANDROID_HOME` environment variable to point at its location.
+Otherwise, here's how to install it:
 
 * Download the "Command line tools" from <https://developer.android.com/studio>.
 * Create a directory `android-sdk/cmdline-tools`, and unzip the command line
@@ -37,11 +41,6 @@ development tools, which currently means Linux or macOS. This involves doing a
 cross-build where you use a "build" Python (for your development machine) to
 help produce a "host" Python for Android.
 
-First, make sure you have all the usual tools and libraries needed to build
-Python for your development machine. The only Android tool you need to install
-is the command line tools package above: the build script will download the
-rest.
-
 The easiest way to do a build is to use the `android.py` script. You can either
 have it perform the entire build process from start to finish in one step, or
 you can do it in discrete steps that mirror running `configure` and `make` for
@@ -80,12 +79,15 @@ call. For example, if you want a pydebug build that also caches the results from
 
 ## Testing
 
-The tests can be run on Linux, macOS, or Windows, although on Windows you'll
-have to build the `cross-build/HOST` subdirectory on one of the other platforms
-and copy it over.
+The test suite can be run on Linux, macOS, or Windows:
 
-The test suite can usually be run on a device with 2 GB of RAM, though for some
-configurations or test orders you may need to increase this. As of Android
+* On Linux, the emulator needs access to the KVM virtualization interface, and
+  a DISPLAY environment variable pointing at an X server.
+* On Windows, you won't be able to do the build on the same machine, so you'll
+  have to copy the `cross-build/HOST` directory from somewhere else.
+
+The test suite can usually be run on a device with 2 GB of RAM, but this is
+borderline, so you may need to increase it to 4 GB. As of Android
 Studio Koala, 2 GB is the default for all emulators, although the user interface
 may indicate otherwise. The effective setting is `hw.ramSize` in
 ~/.android/avd/*.avd/hardware-qemu.ini, whereas Android Studio displays the

Android/android.py

@@ -259,8 +259,8 @@ def setup_testbed():
              f"{temp_dir}/{outer_jar}", "gradle-wrapper.jar"])
 
 
-# run_testbed will build the app automatically, but it hides the Gradle output
-# by default, so it's useful to have this as a separate command for the buildbot.
+# run_testbed will build the app automatically, but it's useful to have this as
+# a separate command to allow running the app outside of this script.
 def build_testbed(context):
     setup_sdk()
     setup_testbed()
@@ -376,6 +376,8 @@ async def find_pid(serial):
     shown_error = False
     while True:
         try:
+            # `pidof` requires API level 24 or higher. The level 23 emulator
+            # includes it, but it doesn't work (it returns all processes).
             pid = (await async_check_output(
                 adb, "-s", serial, "shell", "pidof", "-s", APP_ID
             )).strip()
@@ -407,6 +409,7 @@ async def logcat_task(context, initial_devices):
     serial = await wait_for(find_device(context, initial_devices), startup_timeout)
     pid = await wait_for(find_pid(serial), startup_timeout)
 
+    # `--pid` requires API level 24 or higher.
     args = [adb, "-s", serial, "logcat", "--pid", pid,  "--format", "tag"]
     hidden_output = []
     async with async_process(
@@ -421,11 +424,15 @@ async def logcat_task(context, initial_devices):
                 # such messages, but other components might.
                 level, message = None, line
 
+            # Exclude high-volume messages which are rarely useful.
+            if context.verbose < 2 and "from python test_syslog" in message:
+                continue
+
             # Put high-level messages on stderr so they're highlighted in the
             # buildbot logs. This will include Python's own stderr.
             stream = (
                 sys.stderr
-                if level in ["E", "F"]  # ERROR and FATAL (aka ASSERT)
+                if level in ["W", "E", "F"]  # WARNING, ERROR, FATAL (aka ASSERT)
                 else sys.stdout
             )
 
@@ -573,8 +580,9 @@ def parse_args():
     test = subcommands.add_parser(
         "test", help="Run the test suite")
     test.add_argument(
-        "-v", "--verbose", action="store_true",
-        help="Show Gradle output, and non-Python logcat messages")
+        "-v", "--verbose", action="count", default=0,
+        help="Show Gradle output, and non-Python logcat messages. "
+        "Use twice to include high-volume messages which are rarely useful.")
     device_group = test.add_mutually_exclusive_group(required=True)
     device_group.add_argument(
         "--connected", metavar="SERIAL", help="Run on a connected device. "
@@ -591,6 +599,13 @@ def parse_args():
 
 def main():
     install_signal_handler()
+
+    # Under the buildbot, stdout is not a TTY, but we must still flush after
+    # every line to make sure our output appears in the correct order relative
+    # to the output of our subprocesses.
+    for stream in [sys.stdout, sys.stderr]:
+        stream.reconfigure(line_buffering=True)
+
     context = parse_args()
     dispatch = {"configure-build": configure_build_python,
                 "make-build": make_build_python,