Warn about attempting to push multiple values at once.

lib/index.js

@@ -232,6 +232,8 @@ const Channel = function (bufferLength = 0) {
         order.reject(new TypeError(
           `Can't push 'undefined' to channel, use close instead.`
         ))
+      } else if (arguments.length > 1) {
+        order.reject(new Error(`Can't push more than one value at a time.`))
       } else {
         pushes.push(order)
         setImmediate(processOrders)

test/index.js

@@ -38,7 +38,9 @@ describe(`Channel`, function () {
       assert.equal(await channel.shift(), 0)
     })()
 
-    await channel.push(0, 1, 2)
+    await channel.push(0)
+    await channel.push(1)
+    await channel.push(2)
   })
 
   describe(`from`, function () {
@@ -188,10 +190,9 @@ describe(`Channel object`, function () {
         })().then(() => {
           assert(false)
         }).catch((reason) => {
-          assert.deepEqual(
-            reason,
-            new TypeError(`Can't push 'undefined' to channel, use close instead.`)
-          )
+          assert.deepEqual(reason, new TypeError(
+            `Can't push 'undefined' to channel, use close instead.`
+          ))
         })
       })
 
@@ -203,14 +204,26 @@ describe(`Channel object`, function () {
         })().then(() => {
           assert(false)
         }).catch((reason) => {
-          assert.deepEqual(
-            reason,
-            new TypeError(`Can't push 'undefined' to channel, use close instead.`)
-          )
+          assert.deepEqual(reason, new TypeError(
+            `Can't push 'undefined' to channel, use close instead.`
+          ))
         })
       })
     })
 
+    it(`disallows multiple values`, function () {
+      const channel = Channel()
+
+      return (async () => {
+        await channel.push(0, 1, 2)
+      })().then(() => {
+        assert(false)
+      }).catch((reason) => {
+        assert.deepEqual(reason, new Error(
+          `Can't push more than one value at a time.`))
+      })
+    })
+
     it(`returns a frozen promise`, function () {
       assert.throws(() => {
         Channel().push(0).frozen = false