Add scaffolding for a 'cton-util test' command.

This command accepts files and directories containing test cases to run.
Recursively searches for test files in any directory it is passed.

Actually running tests is not yet implemented.

cranelift/src/tools/filetest/mod.rs

@@ -0,0 +1,33 @@
+//! File tests.
+//!
+//! This module contains the main driver for `cton-util test` as well as implementations of the
+//! available test commands.
+
+use std::path::Path;
+use CommandResult;
+use filetest::runner::TestRunner;
+
+mod runner;
+
+/// Main entry point for `cton-util test`.
+///
+/// Take a list of filenames which can be either `.cton` files or directories.
+///
+/// Files are interpreted as test cases and executed immediately.
+///
+/// Directories are scanned recursively for test cases ending in `.cton`. These test cases are
+/// executed on background threads.
+///
+pub fn run(files: Vec<String>) -> CommandResult {
+    let mut runner = TestRunner::new();
+
+    for path in files.iter().map(Path::new) {
+        if path.is_file() {
+            runner.push_test(path);
+        } else {
+            runner.push_dir(path);
+        }
+    }
+
+    runner.run()
+}