Channel.select: Complain when given non-channel method promises.

lib/index.js

@@ -326,9 +326,10 @@ Channel.select = methodPromises =>
   Object.assign(
     new Promise((resolve, reject) => {
       methodPromises.forEach(async promise => {
+        try {
           promise.prethen(() => {
-          // We've been given a heads-up that this method will complete first so
+            // We've been given a heads-up that this method will complete first
-          // cancel the other method calls.
+            // so cancel the other method calls.
             methodPromises.forEach(other => {
               if (other !== promise) {
                 other.cancel();
@@ -343,6 +344,13 @@ Channel.select = methodPromises =>
           }
 
           resolve(promise.channel);
+        } catch (exception) {
+          reject(
+            new TypeError(
+              `Channel.select accepts only Channel method promises.`
+            )
+          );
+        }
       });
     }),
     {

test/index.js

@@ -128,6 +128,12 @@ describe(`Channel`, function() {
       closed
     );
   });
+
+  it(`complains when given non-channel method promises`, function() {
+    assertRejects(async () => {
+      await Channel.select([Promise.resolve()]);
+    }, new TypeError(`Channel.select accepts only Channel method promises.`));
+  });
 });
 
 describe(`functional interface`, async function() {