Only print cargo test output the once

Also introduces testing of our CLI's output via `assert_cmd`. Expect some follow
ups to get more of our testing infrastructure using this incredible crate!

Fixes #511

tests/all/test.rs

@@ -337,3 +337,43 @@ fn test_output_is_printed_once_in_both_stdout_and_failures() {
             err.matches("YABBA DABBA DOO").count() == log_cnt * 2
         }));
 }
+
+#[test]
+fn test_output_is_printed_once() {
+    let fixture = fixture::Fixture::new();
+    fixture
+        .readme()
+        .cargo_toml("wbg-test-node")
+        .hello_world_src_lib()
+        .file(
+            "tests/node.rs",
+            r#"
+                extern crate wasm_bindgen;
+                extern crate wasm_bindgen_test;
+                use wasm_bindgen::prelude::*;
+                use wasm_bindgen_test::*;
+
+                #[wasm_bindgen]
+                extern {
+                    #[wasm_bindgen(js_namespace = console)]
+                    fn log(s: &str);
+                }
+
+                #[wasm_bindgen_test]
+                fn pass() {
+                    log("YABBA DABBA DOO");
+                    assert_eq!(1, 2);
+                }
+            "#,
+        );
+
+    fixture
+        .wasm_pack()
+        .arg("test")
+        .arg("--node")
+        .assert()
+        .stderr(predicate::function(|err: &str| {
+            err.matches("YABBA DABBA DOO").count() == 1
+        }))
+        .failure();
+}

tests/all/utils/fixture.rs

@@ -289,6 +289,16 @@ impl Fixture {
         cmd
     }
 
+    /// Get a `wasm-pack` command configured to run in this fixure's temp
+    /// directory and using the test cache.
+    pub fn wasm_pack(&self) -> Command {
+        use assert_cmd::prelude::*;
+        let mut cmd = Command::main_binary().unwrap();
+        cmd.current_dir(&self.path);
+        cmd.env("WASM_PACK_CACHE", self.cache_dir());
+        cmd
+    }
+
     pub fn lock(&self) -> MutexGuard<'static, ()> {
         use std::sync::Mutex;
         lazy_static! {