fix: add testnetChannelEndpoint()

web3.js/src/index.js

@@ -13,3 +13,4 @@ export {sendAndConfirmTransaction} from './util/send-and-confirm-transaction';
 export {
   sendAndConfirmRawTransaction,
 } from './util/send-and-confirm-raw-transaction';
+export {testnetChannelEndpoint} from './util/testnet';

web3.js/src/transaction.js

@@ -168,11 +168,13 @@ export class Transaction {
         programIds.push(programId);
       }
 
-      instruction.keys.map(key => key.toString()).forEach(key => {
-        if (!keys.includes(key)) {
-          keys.push(key);
-        }
-      });
+      instruction.keys
+        .map(key => key.toString())
+        .forEach(key => {
+          if (!keys.includes(key)) {
+            keys.push(key);
+          }
+        });
     });
 
     const instructions = this.instructions.map(instruction => {

web3.js/src/util/testnet.js

@@ -0,0 +1,27 @@
+//@flow
+
+import {testnetDefaultChannel} from '../../package.json';
+
+/**
+ * @private
+ */
+const endpoint = {
+  edge: 'https://api.edge.testnet.solana.com',
+  beta: 'https://api.beta.testnet.solana.com',
+  stable: 'https://api.testnet.solana.com',
+};
+
+/**
+ * Retrieves the RPC endpoint URL for the specified testnet release
+ * channel
+ */
+export function testnetChannelEndpoint(channel?: string): string {
+  if (!channel) {
+    return endpoint[testnetDefaultChannel];
+  }
+
+  if (endpoint[channel]) {
+    return endpoint[channel];
+  }
+  throw new Error(`Unknown channel: ${channel}`);
+}