Skip regression 210 test on APFS

APFS does not support creating filenames with invalid UTF-8 byte codes,
thus this test doesn't make sense. Skip it on file systems where this
shouldn't be possible.

Fixes #559

tests/workdir.rs

@@ -41,11 +41,16 @@ impl WorkDir {
         }
     }
 
-    /// Create a new file with the given name and contents in this directory.
+    /// Create a new file with the given name and contents in this directory, or panic on error.
     pub fn create<P: AsRef<Path>>(&self, name: P, contents: &str) {
         self.create_bytes(name, contents.as_bytes());
     }
 
+    /// Try to create a new file with the given name and contents in this directory.
+    pub fn try_create<P: AsRef<Path>>(&self, name: P, contents: &str) -> io::Result<()> {
+        self.try_create_bytes(name, contents.as_bytes())
+    }
+
     /// Create a new file with the given name and size.
     pub fn create_size<P: AsRef<Path>>(&self, name: P, filesize: u64) {
         let path = self.dir.join(name);
@@ -53,12 +58,17 @@ impl WorkDir {
         nice_err(&path, file.set_len(filesize));
     }
 
-    /// Create a new file with the given name and contents in this directory.
+    /// Create a new file with the given name and contents in this directory, or panic on error.
     pub fn create_bytes<P: AsRef<Path>>(&self, name: P, contents: &[u8]) {
         let path = self.dir.join(name);
-        let mut file = nice_err(&path, File::create(&path));
-        nice_err(&path, file.write_all(contents));
-        nice_err(&path, file.flush());
+        nice_err(&path, self.try_create_bytes(&path, contents));
+    }
+
+    /// Try to create a new file with the given name and contents in this directory.
+    fn try_create_bytes<P: AsRef<Path>>(&self, path: P, contents: &[u8]) -> io::Result<()> {
+        let mut file = File::create(&path)?;
+        file.write_all(contents)?;
+        file.flush()
     }
 
     /// Remove a file with the given name from this directory.