add alternative assert function for emscripten

lib/emscripten/tests/emtests/_common.rs

@@ -41,3 +41,44 @@ macro_rules! assert_emscripten_output {
         );
     }};
 }
+
+pub fn assert_emscripten_output(wasm_bytes: &[u8], raw_expected_str: &str) {
+    use wasmer_clif_backend::CraneliftCompiler;
+    use wasmer_emscripten::{
+        EmscriptenGlobals,
+        generate_emscripten_env,
+        stdio::StdioCapturer
+    };
+
+    let module = wasmer_runtime_core::compile_with(&wasm_bytes[..], &CraneliftCompiler::new())
+        .expect("WASM can't be compiled");
+
+    let mut emscripten_globals = EmscriptenGlobals::new(&module);
+    let import_object = generate_emscripten_env(&mut emscripten_globals);
+    let mut instance = module.instantiate(&import_object)
+        .map_err(|err| format!("Can't instantiate the WebAssembly module: {:?}", err)).unwrap();
+
+    let capturer = StdioCapturer::new();
+
+    wasmer_emscripten::run_emscripten_instance(
+        &module,
+        &mut instance,
+    "test",
+    vec![],
+    ).expect("run_emscripten_instance finishes");
+
+    let raw_output_string = capturer.end().unwrap().0;
+
+    // trim the strings to avoid cross-platform line ending and white space issues
+    let output = raw_output_string.trim();
+    let expected_output = raw_expected_str.trim();
+
+    let contains_output = output.contains(expected_output);
+
+   assert!(
+       contains_output,
+       "Output: `{}` does not contain expected output: `{}`",
+       output,
+       expected_output
+   );
+}