diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a6fae81..fb978b2 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -48,11 +48,8 @@ network — nothing in the suite makes an RPC call. Code that talks to a server
 structural fake, as in `test/futility.test.ts`, which stands up an object shaped like `rpc.Server`
 and asserts on which calls it received.
 
-Two things worth knowing before you add a test:
+One thing worth knowing before you add a test:
 
-- **`test/` is not type-checked.** `tsconfig.json` excludes it, so `npm run build` will not catch a
-  type error in a test file. This is a known gap with an open issue against it; until it closes, do
-  not assume a green build means your test compiles under `strict`.
 - **Relative imports need the `.js` extension**, including in tests. The package is
   `"type": "module"` with `moduleResolution: "NodeNext"`, so `../src/keeper/loop.js` is correct even
   though the file on disk is `loop.ts`.
diff --git a/package.json b/package.json
index ca3ea8c..3391c42 100644
--- a/package.json
+++ b/package.json
@@ -15,7 +15,7 @@
     "dist"
   ],
   "scripts": {
-    "build": "tsc -p tsconfig.json",
+    "build": "tsc -p tsconfig.json && tsc -p tsconfig.test.json",
     "lint": "eslint .",
     "format": "prettier --write .",
     "format:check": "prettier --check .",
diff --git a/test/discover.test.ts b/test/discover.test.ts
index 3e30a2a..c1f544e 100644
--- a/test/discover.test.ts
+++ b/test/discover.test.ts
@@ -86,7 +86,12 @@ describe("unwrapPage", () => {
   });
 
   it("throws on an Err, naming the start offset", () => {
-    expect(() => unwrapPage(new contractSpec.Err("LimitTooLarge"), 50)).toThrow(/start=50/);
+    // The SDK types `Err` as wrapping an `ErrorMessage` ({ message }), not a
+    // bare string; `unwrapPage` only stringifies it, so the payload is not
+    // asserted on here.
+    expect(() => unwrapPage(new contractSpec.Err({ message: "LimitTooLarge" }), 50)).toThrow(
+      /start=50/,
+    );
   });
 
   it("throws when the payload is not a list", () => {
diff --git a/test/ttl.test.ts b/test/ttl.test.ts
index ef1c584..a189d06 100644
--- a/test/ttl.test.ts
+++ b/test/ttl.test.ts
@@ -51,7 +51,10 @@ describe("classify", () => {
 
 describe("buildReadings", () => {
   it("pairs each requested key with its entry", () => {
-    const keys = [instanceLedgerKey(CONTRACT), symbolKey("Balance")];
+    const keys: [xdr.LedgerKey, xdr.LedgerKey] = [
+      instanceLedgerKey(CONTRACT),
+      symbolKey("Balance"),
+    ];
     const entries = [
       { key: keys[0], val: {}, liveUntilLedgerSeq: 600_000 },
       { key: keys[1], val: {}, liveUntilLedgerSeq: 150_000 },
@@ -68,7 +71,10 @@ describe("buildReadings", () => {
   });
 
   it("marks a key the RPC omitted as archived", () => {
-    const keys = [instanceLedgerKey(CONTRACT), symbolKey("Milestones")];
+    const keys: [xdr.LedgerKey, xdr.LedgerKey] = [
+      instanceLedgerKey(CONTRACT),
+      symbolKey("Milestones"),
+    ];
     const entries = [{ key: keys[0], val: {}, liveUntilLedgerSeq: 600_000 }];
     const readings = buildReadings(keys, entries, 100_000, 100_000);
 
diff --git a/tsconfig.json b/tsconfig.json
index 27eca11..170bd5d 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -18,5 +18,5 @@
     "forceConsistentCasingInFileNames": true
   },
   "include": ["src/**/*.ts"],
-  "exclude": ["node_modules", "dist", "test"]
+  "exclude": ["node_modules", "dist"]
 }
diff --git a/tsconfig.test.json b/tsconfig.test.json
new file mode 100644
index 0000000..1931d3d
--- /dev/null
+++ b/tsconfig.test.json
@@ -0,0 +1,9 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "noEmit": true,
+    "rootDir": "."
+  },
+  "include": ["test/**/*.ts", "src/**/*.ts"],
+  "exclude": ["node_modules", "dist"]
+}