Fix Windows-only test

testsuite/tests/index/external-msys2/test.py

@@ -1,15 +1,22 @@
 """
-Test that installing msys2 dependency work as expected.
+Test that installing msys2 dependency work as expected. The existence of the
+'dialog' command is checked in a post-fetch action.
 """
 
-from drivers.alr import run_alr
-
+import os
 import platform
+from glob import glob
+
+from drivers.alr import run_alr
 
 if platform.system() == 'Windows':
     # Should silently retrieve everything
-    p = run_alr('--non-interactive', '-v', 'get', 'main',
-                quiet=False, debug=True)
+    run_alr('get', 'main')
+    os.chdir(glob('main*')[0])
+
+    # Trigger post-fetch
+    p = run_alr('build', 'main',
+                quiet=False, debug=True, complain_on_error=False)
 
     checks = 0
     for line in p.out.splitlines():
@@ -19,4 +26,7 @@
 
     assert checks == 1, 'Only %d match in the output : "%s"' % (checks, p.out)
 
-print('SUCCESS')
+    print('SUCCESS')
+
+else:
+    print('SKIP: test is Windows-only')