test: Add a utility for creating null loggers for tests

tests/all/main.rs

@@ -2,6 +2,8 @@ extern crate failure;
 #[macro_use]
 extern crate serde_derive;
 extern crate serde_json;
+#[macro_use]
+extern crate slog;
 extern crate structopt;
 extern crate tempfile;
 extern crate wasm_pack;

tests/all/utils/logger.rs

@@ -0,0 +1,6 @@
+use slog::Logger;
+
+// Create a logger that ignores log messages for testing.
+pub fn null_logger() -> Logger {
+    Logger::root(slog::Discard, o!())
+}

tests/all/utils/mod.rs

@@ -1,3 +1,4 @@
 pub mod file;
 pub mod fixture;
+pub mod logger;
 pub mod manifest;