test/py: mmc: Add 'mmc dev' test

Add separate test for 'mmc dev' subcommand. This tests whether
the system can switch to a specific card.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/py/tests/test_mmc_rd.py b/test/py/tests/test_mmc_rd.py
index 40ae1a8..1337074 100644
--- a/test/py/tests/test_mmc_rd.py
+++ b/test/py/tests/test_mmc_rd.py
@@ -84,6 +84,27 @@
     assert good_response in response
 
 @pytest.mark.buildconfigspec('cmd_mmc')
+def test_mmc_dev(u_boot_console, env__mmc_rd_config):
+    """Test the "mmc dev" command.
+
+    Args:
+        u_boot_console: A U-Boot console connection.
+        env__mmc_rd_config: The single MMC configuration on which
+            to run the test. See the file-level comment above for details
+            of the format.
+
+    Returns:
+        Nothing.
+    """
+
+    is_emmc = env__mmc_rd_config['is_emmc']
+    devid = env__mmc_rd_config['devid']
+    partid = env__mmc_rd_config.get('partid', 0)
+
+    # Select MMC device
+    mmc_dev(u_boot_console, is_emmc, devid, partid)
+
+@pytest.mark.buildconfigspec('cmd_mmc')
 def test_mmc_rd(u_boot_console, env__mmc_rd_config):
     """Test the "mmc read" command.