Add test cases for invoices with longer HRP prefixes

Tests for gh-3456 MAX_PREFIX fix:
- lnbc100u (10,000 sats) - 7 char HRP baseline
- lnbc130130n (13,013 sats) - 11 char HRP, requires MAX_PREFIX > 10

Root cause: Invoices with "odd" sat amounts use nano-BTC encoding
which produces longer HRPs that exceeded old MAX_PREFIX limit.

Related: #3456

Signed-off-by: alltheseas <alltheseas@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

damusTests/InvoiceTests.swift

@@ -197,6 +197,42 @@ final class InvoiceTests: XCTestCase {
         })
     }
 
+    // MARK: - Invoice parsing tests for issue #3456 (MAX_PREFIX fix)
+    // These test invoices with longer HRP prefixes that require MAX_PREFIX > 10
+
+    /// Test invoice from gh-3456: 10,000 sats (100 micro-BTC)
+    /// HRP: lnbc100u (7 chars) - should work with old MAX_PREFIX
+    func testParseInvoice_gh3456_100u() throws {
+        let invstr = "lnbc100u1p55gjvwpp5fgrv9nq4y5turswulpym74rm2q7jnwvqzqr90y4m7xrjyu8025vshp5jxmcdmqe5kp7kcmsngxxejshcqe5pglk5w9rjgk5ltqc3ada5wlscqzzsxqyz5vqsp5f358u7jquhy20cpxq9r6kspcsd46ksgns0zrx028x2csat2cqzrs9qxpqysgqzwsxjn7wmwc2n9yl3h3pu4ph9mma2w7q6f7h8xxhql0d9nxu90087jru6e30t79l6d70rcphsa65kzw6l5kzz2njr777e8e2m80l4ygqjw8mm3"
+
+        guard let invoice = decode_bolt11(invstr) else {
+            XCTFail("Failed to decode invoice - MAX_PREFIX may be too small")
+            return
+        }
+
+        // 100 micro-BTC = 10,000 sats = 10,000,000 millisats
+        XCTAssertEqual(invoice.amount, .specific(10_000_000))
+    }
+
+    /// Test invoice from gh-3456: 13,013 sats (130130 nano-BTC)
+    /// HRP: lnbc130130n (11 chars) - requires MAX_PREFIX > 10
+    func testParseInvoice_gh3456_130130n() throws {
+        let invstr = "lnbc130130n1p5h77tgpp5edwq8elur9e66vhd7wf0s75p20hvppna49dsrchel6xkq69tm4aqdq4w3jhxapqvehhygrzda68xcqzzsxqyz5vqsp56cdkune763pdxqy0jk44hhmv784jzf9m8mk8wspyngq2etehadps9qxpqysgquhrggc6a654gyelax0tcqd9gc9hyajt39t8wksgv0n0jy7q95l4htvgqsydz4fvdlgwa72xqddynsy6k3zq0tmhnxva0dfkhcxduh6gpyl0rgn"
+
+        guard let invoice = decode_bolt11(invstr) else {
+            XCTFail("Failed to decode invoice - MAX_PREFIX may be too small for 11-char HRP")
+            return
+        }
+
+        // 130130 nano-BTC = 13,013 sats = 13,013,000 millisats
+        XCTAssertEqual(invoice.amount, .specific(13_013_000))
+    }
+
+    // Note: Tests for lnbc23450n (2345 sats) and lnbc19710n (1971 sats) would require
+    // real invoice strings. The testParseInvoice_gh3456_130130n test above covers
+    // the 11-char HRP case which exercises the MAX_PREFIX fix more thoroughly than
+    // 10-char HRPs would. If specific test invoices become available, add tests here.
+
     /*
     // gh-3144: It was decided on a standup meeting that we do not need invoices to render, few people use this feature.
     func testParseInvoice() throws {
@@ -229,5 +265,39 @@ final class InvoiceTests: XCTestCase {
         })
     }
     */
+    
+    /// Tests decoding a BOLT11 invoice using the decode_bolt11 function
+    func testDecodeBolt11Invoice() throws {
+        let invstr = "lnbc19710n1p5czpejsp5rmhun0ghrzv9ce0whqn3q2ll8y5kql8mgad90kxlq2zuq784wwuqpp53ks03npkdadza0c8r0qrsgypfx7wsrtr90pqxsgzpcw8yf3358uqhp5vc0usy5w5clt4xwdu6txzgyuxcnyuyd2r6f8ncjacvzrzxtvg50sxq9z0rgqcqpnrzjqt0mfswatysklf4z358sztscs5t0vdghmd5vfe9c9sa0gy6r5pdugrjqtsqqdtcqqyqqqqqqqqqqdpsq8s9qxpqysgq59ja4yg7ayty0cu8etja0unme76d4lm6crzsw5g9uj3h5748xcypwf4ahgyut7vegpz4a6jvq7lj5p8zqutaznjrxgcgnuwejm8cwtsqgzcx97"
+        
+        // Try decoding with lowercase (standard format)
+        var invoice = decode_bolt11(invstr)
+        
+        // If lowercase fails, try uppercase
+        if invoice == nil {
+            invoice = decode_bolt11(invstr.uppercased())
+        }
+        
+        guard let decodedInvoice = invoice else {
+            XCTFail("Failed to decode BOLT11 invoice with both lowercase and uppercase")
+            return
+        }
+        
+        // Verify that the invoice was successfully decoded
+        XCTAssertNotNil(decodedInvoice)
+        
+        // Verify the invoice has a specific amount (19710 nanosatoshis in the invoice string)
+        // Note: The amount is encoded as 1971 * 10 = 19710 nanosatoshis = 1,971,000 millisatoshis
+        switch decodedInvoice.amount {
+        case .specific(let amount):
+            XCTAssertGreaterThan(amount, 0, "Invoice amount should be greater than 0")
+        case .any:
+            XCTFail("Expected specific amount, got .any")
+        }
+        
+        // Verify basic invoice properties exist
+        XCTAssertGreaterThan(decodedInvoice.created_at, 0)
+        XCTAssertGreaterThan(decodedInvoice.expiry, 0)
+    }
 
 }