Added a windows-specific tee equivalent

Author: Michael-F-Bryan

tests/alternate_backends.rs

@@ -4,6 +4,7 @@ extern crate mdbook;
 extern crate tempdir;
 
 use std::fs::File;
+use std::path::Path;
 use tempdir::TempDir;
 use mdbook::config::Config;
 use mdbook::MDBook;
@@ -30,11 +31,22 @@ fn alternate_backend_with_arguments() {
     md.build().unwrap();
 }
 
+/// Get a command which will pipe `stdin` to the provided file.
+fn tee_command<P: AsRef<Path>>(out_file: P) -> String {
+    let out_file = out_file.as_ref();
+
+    if cfg!(windows) {
+        format!("cmd.exe /c type ^> \"{}\"", out_file.display())
+    } else {
+        format!("tee {}", out_file.display())
+    }
+}
+
 #[test]
 fn backends_receive_render_context_via_stdin() {
     let temp = TempDir::new("output").unwrap();
     let out_file = temp.path().join("out.txt");
-    let cmd = format!("tee {}", out_file.display());
+    let cmd = tee_command(&out_file);
 
     let (md, _temp) = dummy_book_with_backend("cat-to-file", &cmd);