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

lib/index.js

@@ -326,23 +326,31 @@ Channel.select = methodPromises =>
   Object.assign(
     new Promise((resolve, reject) => {
       methodPromises.forEach(async promise => {
-        promise.prethen(() => {
-          // We've been given a heads-up that this method will complete first so
-          // cancel the other method calls.
-          methodPromises.forEach(other => {
-            if (other !== promise) {
-              other.cancel();
-            }
-          });
-        });
-
         try {
-          await promise;
+          promise.prethen(() => {
-        } catch (exception) {
+            // We've been given a heads-up that this method will complete first
-          reject(exception);
+            // so cancel the other method calls.
-        }
+            methodPromises.forEach(other => {
+              if (other !== promise) {
+                other.cancel();
+              }
+            });
+          });
 
-        resolve(promise.channel);
+          try {
+            await promise;
+          } catch (exception) {
+            reject(exception);
+          }
+
+          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() {