tests: Create the ScopedFile type for temporary files in tests

This commit adds the `ScopedFile` type, which wraps and derefs to a `File`. When
a `ScopedFile` is dropped, it removes the underlying file from the
filesystem. This is useful for temporary, generated files in tests.

tests/common/util.rs

@@ -5,6 +5,7 @@ extern crate tempdir;
 use std::env;
 use std::fs::{self, File};
 use std::io::{Read, Write, Result};
+use std::ops::{Deref, DerefMut};
 #[cfg(unix)]
 use std::os::unix::fs::symlink as symlink_file;
 #[cfg(windows)]
@@ -122,6 +123,40 @@ pub fn recursive_copy(src: &Path, dest: &Path) -> Result<()> {
     Ok(())
 }
 
+/// A scoped, temporary file that is removed upon drop.
+pub struct ScopedFile {
+    path: PathBuf,
+    file: File,
+}
+
+impl ScopedFile {
+    fn new(path: PathBuf, file: File) -> ScopedFile {
+        ScopedFile {
+            path: path,
+            file: file
+        }
+    }
+}
+
+impl Deref for ScopedFile {
+    type Target = File;
+    fn deref(&self) -> &File {
+        &self.file
+    }
+}
+
+impl DerefMut for ScopedFile {
+    fn deref_mut(&mut self) -> &mut File {
+        &mut self.file
+    }
+}
+
+impl Drop for ScopedFile {
+    fn drop(&mut self) {
+        fs::remove_file(&self.path).unwrap();
+    }
+}
+
 pub struct AtPath {
     pub subdir: PathBuf,
 }
@@ -185,6 +220,9 @@ impl AtPath {
             Err(e) => panic!("{}", e),
         }
     }
+    pub fn make_scoped_file(&self, name: &str) -> ScopedFile {
+        ScopedFile::new(self.plus(name), self.make_file(name))
+    }
     pub fn touch(&self, file: &str) {
         log_info("touch", self.plus_as_string(file));
         File::create(&self.plus(file)).unwrap();