diff --git a/packages/stellar-sdk-helpers/src/keeper-tx.test.ts b/packages/stellar-sdk-helpers/src/keeper-tx.test.ts
new file mode 100644
index 0000000..62a6f6c
--- /dev/null
+++ b/packages/stellar-sdk-helpers/src/keeper-tx.test.ts
@@ -0,0 +1,137 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  STALE_ADAPTER_MESSAGE,
+  StaleAdapterError,
+  SubmissionFailedError,
+  SubmissionInFlightError,
+  expectString,
+  isDefinitiveOnChainFailure,
+  isStaleAdapterError,
+  isTransientKeeperError,
+  rawErrorText,
+} from "./keeper-tx";
+
+const HASH = "a".repeat(64);
+
+describe("rawErrorText", () => {
+  it("keeps every line of an Error message", () => {
+    // The whole point of this over errorMessage(): a status code on a later
+    // line still has to be visible to the classifiers below.
+    expect(rawErrorText(new Error("wrapped fetch failure\nstatus 503"))).toBe(
+      "wrapped fetch failure\nstatus 503"
+    );
+  });
+
+  it("stringifies a non-Error throw", () => {
+    expect(rawErrorText("plain string")).toBe("plain string");
+    expect(rawErrorText(undefined)).toBe("undefined");
+  });
+});
+
+describe("isDefinitiveOnChainFailure", () => {
+  it("matches waitForTransaction's confirmed-failure message", () => {
+    expect(
+      isDefinitiveOnChainFailure(
+        new Error(`Transaction ${HASH} failed on-chain`)
+      )
+    ).toBe(true);
+  });
+
+  it("does not match its timeout message, whose outcome is still unknown", () => {
+    expect(
+      isDefinitiveOnChainFailure(
+        new Error(`Timed out waiting for transaction ${HASH} to confirm`)
+      )
+    ).toBe(false);
+  });
+});
+
+describe("isTransientKeeperError", () => {
+  it("is false for a SubmissionFailedError regardless of its message text", () => {
+    // Confirmed failed on-chain: resubmitting has no reason to succeed, even
+    // though the wrapped message happens to contain a transient keyword.
+    expect(
+      isTransientKeeperError(
+        new SubmissionFailedError(new Error("timed out; rate limit 503"))
+      )
+    ).toBe(false);
+  });
+
+  it("is true for a SubmissionInFlightError, whose real outcome is unknown", () => {
+    expect(
+      isTransientKeeperError(
+        new SubmissionInFlightError(HASH, new Error("socket hang up"))
+      )
+    ).toBe(true);
+  });
+
+  it("matches transient keywords case-insensitively", () => {
+    expect(isTransientKeeperError(new Error("Please try again"))).toBe(true);
+    expect(isTransientKeeperError(new Error("Request TIMEOUT"))).toBe(true);
+    expect(isTransientKeeperError(new Error("Timed Out waiting"))).toBe(true);
+    expect(isTransientKeeperError(new Error("Rate Limit exceeded"))).toBe(true);
+    expect(isTransientKeeperError(new Error("temporarily unavailable"))).toBe(
+      true
+    );
+  });
+
+  it("matches retryable HTTP status codes on word boundaries", () => {
+    for (const code of [429, 500, 502, 503, 504]) {
+      expect(isTransientKeeperError(new Error(`HTTP ${code}`))).toBe(true);
+    }
+  });
+
+  it("ignores those digits inside a longer number", () => {
+    // An amount or ledger number that merely contains 503 is not a status
+    // code, and misreading it would retry a permanent failure forever.
+    expect(isTransientKeeperError(new Error("ledger 15034 rejected"))).toBe(
+      false
+    );
+    expect(isTransientKeeperError(new Error("amount 4290000 too low"))).toBe(
+      false
+    );
+  });
+
+  it("is false for an unrelated permanent error", () => {
+    expect(isTransientKeeperError(new Error("Simulation failed: auth"))).toBe(
+      false
+    );
+    expect(isTransientKeeperError("not an error at all")).toBe(false);
+  });
+});
+
+describe("expectString", () => {
+  it("returns a string value unchanged", () => {
+    expect(expectString("CVAULT", "get_adapter", "CCONTRACT")).toBe("CVAULT");
+  });
+
+  it("throws a message naming the method, contract, and actual type", () => {
+    expect(() => expectString(null, "get_adapter", "CCONTRACT")).toThrow(
+      "get_adapter() on CCONTRACT did not return a string (got object)"
+    );
+    expect(() => expectString(42, "get_adapter", "CCONTRACT")).toThrow(
+      "(got number)"
+    );
+    expect(() => expectString(undefined, "get_adapter", "CCONTRACT")).toThrow(
+      "(got undefined)"
+    );
+  });
+});
+
+describe("isStaleAdapterError", () => {
+  it("detects a StaleAdapterError by message, not by instanceof", () => {
+    // withKeeperRetry rewraps errors and loses the original type, so the
+    // guard has to survive being carried across as plain message text.
+    const err = new StaleAdapterError("CEXPECTED", "CACTUAL");
+    expect(isStaleAdapterError(err)).toBe(true);
+    expect(isStaleAdapterError(new Error(err.message))).toBe(true);
+    expect(err.message).toContain(STALE_ADAPTER_MESSAGE);
+    expect(err.message).toContain("CEXPECTED");
+    expect(err.message).toContain("CACTUAL");
+  });
+
+  it("is false for any other error", () => {
+    expect(isStaleAdapterError(new Error("Simulation failed"))).toBe(false);
+  });
+});