fix: add testnetChannelEndpoint()

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}`);
+}