payment tests

tests/ShouldParseEurcChains/main.cpp

@@ -65,6 +65,27 @@ int main() {
           "eurc: numeric result rejected — the wire type is a hex string");
     Check(!ParseEthCallUint("garbage").has_value(), "eurc: malformed payload");
 
+    // The OUTBOUND half of the balance check, byte for byte: selector, then
+    // the address left-padded into exactly one 32-byte ABI word — 24 zero hex
+    // digits (12 bytes), then the 40 address digits. Pinned as a literal
+    // because this line once padded 24 BYTES instead of 12: the address slid
+    // past the argument word, every node cleanly answered balanceOf of a
+    // zero-balance garbage address, and paid orders read as unpaid forever —
+    // no error on either side. A wrong length here is money-losing even when
+    // every reply parses.
+    {
+        const std::string data = Server::BalanceOfCallData(
+            "0x311660cfd1d0c35616cf6dfc3932881b22bb46ec");
+        Check(data ==
+                  "0x70a08231"
+                  "000000000000000000000000"
+                  "311660cfd1d0c35616cf6dfc3932881b22bb46ec",
+              "eurc: balanceOf calldata is selector + one 32-byte word", data);
+        Check(data.size() == 2 + 8 + 64,
+              "eurc: balanceOf calldata is exactly 4 + 32 bytes",
+              std::to_string(data.size()));
+    }
+
     const auto chains = Server::ParseEurcChains(R"({"chains":[
         {"name":"base","rpc":"https://mainnet.base.org",
          "contract":"0x60a3E35Cc302bFA44Cb288Bc5a4F316Fdb1adb42",