X wcfs: tests: Print which files are still opened on wcfs if `fusermount -u` fails

Helps to understand why if wcfs cannot be unmounted.

wcfs/wcfs_test.py

@@ -104,10 +104,26 @@ def setup_function(f):
 def teardown_function(f):
     mounted = is_mountpoint(testmntpt)
     if mounted:
-        subprocess.check_call(["fusermount", "-u", testmntpt])
+        fuse_unmount(testmntpt)
     if os.path.exists(testmntpt):
         os.rmdir(testmntpt)
 
+# fuse_unmount unmounts FUSE filesystem mounted @ mntpt.
+@func
+def fuse_unmount(mntpt):
+    assert is_mountpoint(mntpt)
+    try:
+        subprocess.check_call(["fusermount", "-u", mntpt])
+    except subprocess.CalledProcessError:
+        # unmount failed, usually due to "device is busy".
+        # Print which files are still opened and reraise
+        def _():
+            print("# lsof %s" % mntpt)
+            subprocess.check_call(["lsof", mntpt])
+        defer(_)
+        raise
+
+
 
 # ---- test join/autostart ----
 
@@ -257,7 +273,7 @@ class tWCFS(_tWCFS):
             # /proc/mounts and avoid `assert not is_mountpoint` above.
             def _():
                 if is_mountpoint(t.wc.mountpoint):
-                    subprocess.check_call(["fusermount", "-u", t.wc.mountpoint])
+                    fuse_unmount(t.wc.mountpoint)
             defer(_)
 
             eprint("\nC: wcfs.go does not exit")
@@ -280,7 +296,7 @@ class tWCFS(_tWCFS):
             #if not ready(t._wcfuseaborted):    XXX kill _wcfuseaborted ?
             #    assert 0 == subprocess.call(["mountpoint", "-q", t.wc.mountpoint])
             assert is_mountpoint(t.wc.mountpoint)
-            subprocess.check_call(["fusermount", "-u", t.wc.mountpoint])
+            fuse_unmount(t.wc.mountpoint)
         defer(_)
 
         t.wc.close()