bitcoin: Add a test for matching on network

    
Add a test module showing how external users are able to
match on `Network` and `Network::Testnet(TestnetVersion)`.
    
This topic is contentious so it helps to show exactly what is possible
and what is not.

Author: tcharding

bitcoin/tests/network.rs

@@ -0,0 +1,74 @@
+//! Tests what a user can do when pattern matching on `Network` and associated types.
+
+use bitcoin::network::{Network, NetworkKind, TestnetVersion};
+
+#[test]
+fn can_match_exhaustively_on_network() {
+    // Returns true if `n` is mainnet.
+    fn is_mainnet(n: Network) -> bool {
+        matches!(n, Network::Bitcoin)
+    }
+
+    assert!(is_mainnet(Network::Bitcoin));
+}
+
+#[test]
+fn can_match_exhaustively_on_testnet() {
+    // Returns true if `n` is any testnet.
+    fn is_testnet(n: Network) -> bool {
+        matches!(n, Network::Testnet(_))
+    }
+
+    assert!(is_testnet(Network::Testnet(TestnetVersion::V3)));
+}
+
+#[test]
+fn can_use_network_kind() {
+    // Returns true if `n` is any mainnet.
+    fn is_mainnet(n: Network) -> bool {
+        NetworkKind::from(n).is_mainnet()
+    }
+
+    // Returns true if `n` is a any testnet.
+    fn is_testnet(n: Network) -> bool {
+        !NetworkKind::from(n).is_mainnet()
+    }
+
+    assert!(is_mainnet(Network::Bitcoin));
+    assert!(!is_testnet(Network::Bitcoin));
+
+    assert!(is_testnet(Network::Testnet(TestnetVersion::V3)));
+    assert!(!is_mainnet(Network::Testnet(TestnetVersion::V3)));
+
+}
+
+#[test]
+fn can_not_match_exaustively_on_testnet_version() {
+    // Returns true if `n` is testnet version 3.
+    fn is_testnet_v3(n: Network) -> bool {
+        match n {
+            Network::Testnet(TestnetVersion::V3) => true,
+            Network::Testnet(TestnetVersion::V4) => false,
+            // Catchall because of `non_exhaustive` attribute.
+            Network::Testnet(_) => false,
+            _ => false,
+        }
+    }
+
+    assert!(is_testnet_v3(Network::Testnet(TestnetVersion::V3)));
+}
+
+#[test]
+fn can_match_on_testnet_version_3_only() {
+    // Returns true if `n` is testnet version 3.
+    fn is_testnet_v3(n: Network) -> bool {
+        match n {
+            Network::Testnet(TestnetVersion::V3) => true,
+            // Catchall because its logically correct to do so.
+            Network::Testnet(_) => false,
+            _ => false,
+        }
+    }
+
+    assert!(is_testnet_v3(Network::Testnet(TestnetVersion::V3)));
+}