test: a token scale of zero decimals is used, not skipped (closes #325)

resolveTokenDecimals() treats a scale of 0 from the bundled list or a
tracked token as an answer, but nothing tested it: changing either
`d !== null` check to a plain truthiness check left every test green
while a zero-decimal token fell through to the next source or to
"decimals unknown".

The approval tests now assert a scale of 0 from each source, both from
the resolver and on the approval screen's Amount line. toDecimals() was
already shared from transferAmount.js since #349.

Model: opus-5-5

tests/approvalAmount.test.js

@@ -31,11 +31,15 @@ const iface = new Interface(ERC20_ABI);
 const NOVEL_TOKEN = "0xE2E0000000000000000000000000000000000E2e";
 // In the bundled list, at 6 decimals.
 const USDC = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48";
+// In the bundled list, at 0 decimals.
+const SLP = "0xCC8Fa225D80b9c7D42F96e9570156c65D6cAAa25";
 const RECIPIENT = "0xC0FfEE0000000000000000000000000000c0fFEe";
 const SPENDER = "0x1111111111111111111111111111111111111111";
 
 // 5,000 units of a 6-decimal token, the amount from the issue.
 const FIVE_THOUSAND_AT_SIX = 5000000000n;
+// 5,000 units of a 0-decimal token, which are 5,000 tokens.
+const FIVE_THOUSAND_AT_ZERO = 5000n;
 const MAX_UINT256 = (1n << 256n) - 1n;
 
 function transferData(amount) {
@@ -113,6 +117,21 @@ describe("resolveTokenDecimals", () => {
         expect(resolveTokenDecimals(NOVEL_TOKEN, state)).toBe(6);
     });
 
+    // Zero decimals is a real scale, not a missing one, so a source that
+    // answers 0 is used rather than fallen past like the unusable entry above.
+    test("uses a bundled scale of zero", () => {
+        state.trackedTokens = [{ address: SLP, symbol: "SLP", decimals: 18 }];
+        expect(resolveTokenDecimals(SLP, state)).toBe(0);
+    });
+
+    test("uses a tracked scale of zero", () => {
+        state.trackedTokens = [
+            { address: NOVEL_TOKEN, symbol: "NOVEL", decimals: 0 },
+        ];
+        state.wallets = walletsHolding(NOVEL_TOKEN, 18);
+        expect(resolveTokenDecimals(NOVEL_TOKEN, state)).toBe(0);
+    });
+
     test("refuses a scale the explorer's own entries disagree about", () => {
         const wallets = walletsHolding(NOVEL_TOKEN, 6);
         wallets[0].addresses.push({
@@ -213,6 +232,21 @@ describe("decodeCalldata amount", () => {
         );
     });
 
+    test("a bundled token with zero decimals shows the true quantity", () => {
+        expect(amountLine(transferData(FIVE_THOUSAND_AT_ZERO), SLP)).toBe(
+            "5000.0000 SLP",
+        );
+    });
+
+    test("a tracked token with zero decimals shows the true quantity", () => {
+        state.trackedTokens = [
+            { address: NOVEL_TOKEN, symbol: "NOVEL", decimals: 0 },
+        ];
+        expect(
+            amountLine(transferData(FIVE_THOUSAND_AT_ZERO), NOVEL_TOKEN),
+        ).toBe("5000.0000 NOVEL");
+    });
+
     test("the amount carried to the status screens is the same string", () => {
         const decoded = decodeCalldata(
             transferData(FIVE_THOUSAND_AT_SIX),