Test support of pyserial external dependency of ESP32 platform

Although Arduino boards platforms traditionally have bundled all dependencies, the ESP32 boards platform expects the
pyserial Python package to be preinstalled on Linux systems.

Although there is already test coverage and support for user installation of arbitrary Python package dependencies of a
platform, the situation is more complex when it comes to this important boards platform. The problem is that there is an
established use pattern that should be supported to avoid breaking user workflows.

The added test checks for regressions in that support.

Author: per1234

.github/workflows/test-integration.yml

@@ -231,6 +231,35 @@ jobs:
             - ${{ env.TESTDATA_SKETCHES_PATH }}/BareMinimum
 
 
+  # Targeted testing for ESP32 boards platform support.
+  pyserial-dependency:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout local repo
+        uses: actions/checkout@v3
+
+      - name: Install pyserial
+        run: |
+          # Use of pip3 and omission of recommended flags done to reproduce established use pattern:
+          # https://github.com/arduino-libraries/ArduinoIoTCloud/blob/1.11.0/.github/workflows/compile-examples.yml#L206
+          pip3 install pyserial
+
+      - name: Run action with board that has pyserial dependency
+        # Use action from local path
+        uses: ./
+        with:
+          platforms: |
+            - name: arduino:avr
+            - source-path: ${{ env.TESTDATA_PLATFORMS_PATH }}/PyserialDependent
+              name: PyserialDependent:avr
+          fqbn: PyserialDependent:avr:pyserial_dependent
+          libraries: |
+            []
+          sketch-paths: |
+            - ${{ env.TESTDATA_SKETCHES_PATH }}/BareMinimum
+
+
   check-sketches-reports:
     needs: all-inputs
     runs-on: ubuntu-latest

.github/workflows/testdata/platforms/PyserialDependent/boards.txt

@@ -0,0 +1,8 @@
+pyserial_dependent.name=pyserial Dependent Board
+pyserial_dependent.upload.maximum_size=32256
+pyserial_dependent.upload.maximum_data_size=2048
+pyserial_dependent.build.mcu=atmega328p
+pyserial_dependent.build.f_cpu=16000000L
+pyserial_dependent.build.board=FOO
+pyserial_dependent.build.core=arduino:arduino
+pyserial_dependent.build.variant=arduino:standard

.github/workflows/testdata/platforms/PyserialDependent/platform.txt

@@ -0,0 +1,5 @@
+name=pyserial Dependent Platform
+version=0.0.0
+# python3 is used to parallel ESP32 platform configuration:
+# https://github.com/espressif/arduino-esp32/blob/2.0.7/platform.txt#L220
+recipe.hooks.prebuild.1.pattern=python3 -c 'import serial'