diff --git a/pkg/spec/test/folio-submit-balance-predicate.test.ts b/pkg/spec/test/folio-submit-balance-predicate.test.ts
new file mode 100644
index 0000000..b3cb5e0
--- /dev/null
+++ b/pkg/spec/test/folio-submit-balance-predicate.test.ts
@@ -0,0 +1,114 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+
+import { submitChangesBalanceByTypedAmount } from "../../../examples/folio/sanderling/predicates.ts";
+
+const submitOn = "testTag:LedgerScreen > testTag:TxnSubmit";
+
+test("single submit: delta matches typed amount", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: { kind: "Tap", on: submitOn },
+      typedAmount: 500,
+      prevTotalBalance: 1000,
+      currTotalBalance: 1500,
+    }),
+    true,
+  );
+});
+
+test("double submit: delta is twice the typed amount, fires", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: { kind: "Tap", on: submitOn },
+      typedAmount: 500,
+      prevTotalBalance: 1000,
+      currTotalBalance: 2000,
+    }),
+    false,
+  );
+});
+
+test("DoubleTap kind also caught when delta exceeds typed amount", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: { kind: "DoubleTap", on: submitOn },
+      typedAmount: 500,
+      prevTotalBalance: 0,
+      currTotalBalance: 1000,
+    }),
+    false,
+  );
+});
+
+test("wrong action kind: vacuous true even with mismatch", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: { kind: "InputText", on: submitOn },
+      typedAmount: 500,
+      prevTotalBalance: 1000,
+      currTotalBalance: 1000,
+    }),
+    true,
+  );
+});
+
+test("wrong target: vacuous true even with mismatch", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: { kind: "Tap", on: "testTag:LoginScreen > testTag:LoginSubmit" },
+      typedAmount: 500,
+      prevTotalBalance: 1000,
+      currTotalBalance: 1000,
+    }),
+    true,
+  );
+});
+
+test("null lastAction: vacuous true", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: null,
+      typedAmount: 500,
+      prevTotalBalance: 1000,
+      currTotalBalance: 2000,
+    }),
+    true,
+  );
+});
+
+test("zero typedAmount: vacuous true", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: { kind: "Tap", on: submitOn },
+      typedAmount: 0,
+      prevTotalBalance: 1000,
+      currTotalBalance: 1500,
+    }),
+    true,
+  );
+});
+
+test("selector as object: coerced safely and TxnSubmit detected", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: { kind: "Tap", on: { testTag: "TxnSubmit" } },
+      typedAmount: 500,
+      prevTotalBalance: 0,
+      currTotalBalance: 1000,
+    }),
+    false,
+  );
+});
+
+test("selector as object without TxnSubmit: vacuous true", () => {
+  assert.equal(
+    submitChangesBalanceByTypedAmount({
+      lastAction: { kind: "Tap", on: { testTag: "LoginSubmit" } },
+      typedAmount: 500,
+      prevTotalBalance: 0,
+      currTotalBalance: 1000,
+    }),
+    true,
+  );
+});