feat: add --network testnet default setting

Similar to how we support `--network futurenet` before you even set it.

No need to make people go look it up on https://developers.stellar.org/docs/reference/networks

cmd/crates/soroban-test/tests/it/config.rs

@@ -42,6 +42,36 @@ fn set_and_remove_network() {
     });
 }
 
+#[test]
+fn use_default_futurenet() {
+    TestEnv::with_default(|sandbox| {
+        sandbox
+            .new_assert_cmd("keys")
+            .args(["generate", "alice", "--network", "futurenet"])
+            .assert()
+            .success();
+        let dir = sandbox.dir().join(".soroban").join("network");
+        let mut read_dir = std::fs::read_dir(dir).unwrap();
+        let file = read_dir.next().unwrap().unwrap();
+        assert_eq!(file.file_name().to_str().unwrap(), "futurenet.toml");
+    });
+}
+
+#[test]
+fn use_default_testnet() {
+    TestEnv::with_default(|sandbox| {
+        sandbox
+            .new_assert_cmd("keys")
+            .args(["generate", "alice", "--network", "testnet"])
+            .assert()
+            .success();
+        let dir = sandbox.dir().join(".soroban").join("network");
+        let mut read_dir = std::fs::read_dir(dir).unwrap();
+        let file = read_dir.next().unwrap().unwrap();
+        assert_eq!(file.file_name().to_str().unwrap(), "testnet.toml");
+    });
+}
+
 fn add_network(sandbox: &TestEnv, name: &str) {
     sandbox
         .new_assert_cmd("network")

cmd/soroban-cli/src/commands/config/locator.rs

@@ -204,10 +204,18 @@ impl Args {
     pub fn read_network(&self, name: &str) -> Result<Network, Error> {
         let res = KeyType::Network.read_with_global(name, &self.local_config()?);
         if let Err(Error::ConfigMissing(_, _)) = &res {
-            if name == "futurenet" {
-                let network = Network::futurenet();
-                self.write_network(name, &network)?;
-                return Ok(network);
+            match name {
+                "futurenet" => {
+                    let network = Network::futurenet();
+                    self.write_network(name, &network)?;
+                    return Ok(network);
+                }
+                "testnet" => {
+                    let network = Network::testnet();
+                    self.write_network(name, &network)?;
+                    return Ok(network);
+                }
+                _ => {}
             }
         }
         res

cmd/soroban-cli/src/commands/network/mod.rs

@@ -249,6 +249,12 @@ impl Network {
 
 impl Network {
     pub fn futurenet() -> Self {
+        Network {
+            rpc_url: "https://soroban-testnet.stellar.org".to_owned(),
+            network_passphrase: "Test SDF Network ; September 2015".to_owned(),
+        }
+    }
+    pub fn testnet() -> Self {
         Network {
             rpc_url: "https://rpc-futurenet.stellar.org:443".to_owned(),
             network_passphrase: "Test SDF Future Network ; October 2022".to_owned(),