fakewallet values in config (#470)

* chore: add fakewallet defaults to config

crates/cdk-mintd/example.config.toml

@@ -55,3 +55,10 @@ ln_backend = "cln"
 # address = ""
 # macaroon_file = ""
 # cert_file = ""
+
+# [fake_wallet]
+# supported_units = ["sat"]
+# fee_percent = 0.02
+# reserve_fee_min = 1
+# min_delay_time = 1
+# max_delay_time = 3

crates/cdk-mintd/src/config.rs

@@ -206,12 +206,32 @@ impl Settings {
         let settings: Settings = config.try_deserialize()?;
 
         match settings.ln.ln_backend {
-            LnBackend::Cln => assert!(settings.cln.is_some()),
-            LnBackend::Strike => assert!(settings.strike.is_some()),
-            LnBackend::LNbits => assert!(settings.lnbits.is_some()),
-            LnBackend::Phoenixd => assert!(settings.phoenixd.is_some()),
-            LnBackend::Lnd => assert!(settings.lnd.is_some()),
-            LnBackend::FakeWallet => (),
+            LnBackend::Cln => assert!(
+                settings.cln.is_some(),
+                "CLN backend requires a valid config."
+            ),
+            LnBackend::Strike => assert!(
+                settings.strike.is_some(),
+                "Strike backend requires a valid config."
+            ),
+            LnBackend::LNbits => assert!(
+                settings.lnbits.is_some(),
+                "LNbits backend requires a valid config"
+            ),
+            LnBackend::Phoenixd => assert!(
+                settings.phoenixd.is_some(),
+                "Phoenixd backend requires a valid config"
+            ),
+            LnBackend::Lnd => {
+                assert!(
+                    settings.lnd.is_some(),
+                    "LND backend requires a valid config."
+                )
+            }
+            LnBackend::FakeWallet => assert!(
+                settings.fake_wallet.is_some(),
+                "FakeWallet backend requires a valid config."
+            ),
         }
 
         Ok(settings)