Add unit tests for USB SD card reader detection

Add comprehensive unit tests for the new USB SD card reader detection
functionality in MediacardComboStorage:

- test_mediacard_combo_storage_usb_sd_card_reader_insertion: Tests
  detection of insertion via capacity change messages
- test_mediacard_combo_storage_usb_sd_card_reader_removal: Tests
  detection of removal via capacity change to 0
- test_mediacard_combo_storage_usb_sd_card_reader_partition: Tests
  extraction of partition names from sda: sda1 patterns
- test_mediacard_combo_storage_usb_sd_card_reader_action_update: Tests
  that action state can be updated from removal to insertion

These tests cover the new code paths added to support USB SD card
readers that appear as SCSI/USB mass storage devices.

Author: chochien

checkbox-support/checkbox_support/tests/test_run_watcher.py

@@ -420,6 +420,47 @@ def test_mediacard_combo_storage_parse_journal_line(self):
         mediacard_combo_storage._parse_journal_line(line_str)
         self.assertEqual(mediacard_combo_storage.action, None)
 
+    def test_mediacard_combo_storage_usb_sd_card_reader_insertion(self):
+        # Test USB SD card reader insertion detection
+        line_str = "sda: detected capacity change from 0 to 31116288"
+        mediacard_combo_storage = MediacardComboStorage("mediacard_combo")
+        mediacard_combo_storage._parse_journal_line(line_str)
+        self.assertEqual(mediacard_combo_storage.action, "insertion")
+        self.assertEqual(
+            mediacard_combo_storage.device, "SD/MMC via USB reader"
+        )
+
+    def test_mediacard_combo_storage_usb_sd_card_reader_removal(self):
+        # Test USB SD card reader removal detection
+        line_str = "sda: detected capacity change from 31116288 to 0"
+        mediacard_combo_storage = MediacardComboStorage("mediacard_combo")
+        mediacard_combo_storage._parse_journal_line(line_str)
+        self.assertEqual(mediacard_combo_storage.action, "removal")
+
+    def test_mediacard_combo_storage_usb_sd_card_reader_partition(self):
+        # Test partition extraction for USB SD card reader
+        line_str = " sda: sda1"
+        mediacard_combo_storage = MediacardComboStorage("mediacard_combo")
+        mediacard_combo_storage._parse_journal_line(line_str)
+        self.assertEqual(mediacard_combo_storage.mounted_partition, "sda1")
+
+    def test_mediacard_combo_storage_usb_sd_card_reader_action_update(self):
+        # Test that action can be updated (removal then insertion)
+        mediacard_combo_storage = MediacardComboStorage("mediacard_combo")
+
+        # First detect removal
+        line_str = "sda: detected capacity change from 31116288 to 0"
+        mediacard_combo_storage._parse_journal_line(line_str)
+        self.assertEqual(mediacard_combo_storage.action, "removal")
+
+        # Then detect insertion - action should update
+        line_str = "sda: detected capacity change from 0 to 31116288"
+        mediacard_combo_storage._parse_journal_line(line_str)
+        self.assertEqual(mediacard_combo_storage.action, "insertion")
+        self.assertEqual(
+            mediacard_combo_storage.device, "SD/MMC via USB reader"
+        )
+
     def test_thunderbolt_storage_init(self):
         thunderbolt_storage = ThunderboltStorage("thunderbolt")
         self.assertEqual(thunderbolt_storage.storage_type, "thunderbolt")