Merge pull request #41 from alexcrichton/on-thread-on-wasm

Default to single-threaded tests for WebAssembly

src/lib.rs

@@ -481,7 +481,7 @@ pub fn run(args: &Arguments, mut tests: Vec<Trial>) -> Conclusion {
 
     // Execute all tests.
     let test_mode = !args.bench;
-    if args.test_threads == Some(1) {
+    if platform_defaults_to_one_thread() || args.test_threads == Some(1) {
         // Run test sequentially in main thread
         for test in tests {
             // Print `test foo    ...`, run the test, then print the outcome in
@@ -537,6 +537,13 @@ pub fn run(args: &Arguments, mut tests: Vec<Trial>) -> Conclusion {
     conclusion
 }
 
+/// Returns whether the current host platform should use a single thread by
+/// default rather than a thread pool by default. Some platforms, such as
+/// WebAssembly, don't have native support for threading at this time.
+fn platform_defaults_to_one_thread() -> bool {
+    cfg!(target_family = "wasm")
+}
+
 /// Runs the given runner, catching any panics and treating them as a failed test.
 fn run_single(runner: Box<dyn FnOnce(bool) -> Outcome + Send>, test_mode: bool) -> Outcome {
     use std::panic::{catch_unwind, AssertUnwindSafe};