diff --git a/package.json b/package.json
index 9c44d41..47c5081 100644
--- a/package.json
+++ b/package.json
@@ -7,6 +7,7 @@
       "@babel/cli": "^7.6.4",
       "@babel/core": "^7.6.4",
       "@babel/preset-env": "^7.6.3",
+      "@types/jest": "^24.0.19",
       "@types/lodash": "^4.14.144",
       "babel-jest": "^24.9.0",
       "jest": "^24.9.0",
diff --git a/src/splat.test.js b/src/splat.test.ts
similarity index 81%
rename from src/splat.test.js
rename to src/splat.test.ts
index 57ac5bf..abbd335 100644
--- a/src/splat.test.js
+++ b/src/splat.test.ts
@@ -1,13 +1,13 @@
 import updux from '.';
 import u from 'updeep';
 
-const tracer = chr => u({ tracer: s => (s||'') + chr });
+const tracer = (chr:string) => u({ tracer: (s='') => s + chr });
 
 test( 'mutations, simple', () => {
     const dux = updux({
         mutations: {
             foo: () => tracer('a'),
-            '*': (p,a) => tracer('b'),
+            '*': () => tracer('b'),
         },
     });
 
@@ -28,14 +28,14 @@ test( 'with subduxes', () => {
     const dux = updux({
         mutations: {
             foo: () => tracer('a'),
-            '*': (dummy,a) => tracer('b'),
-            bar: () => ({bar}) => ({ bar, tracer: bar.tracer })
+            '*': () => tracer('b'),
+            bar: () => ({bar}:any) => ({ bar, tracer: bar.tracer })
         },
         subduxes: {
             bar: updux({
                 mutations: {
                     foo: () => tracer('d'),
-                    '*': (dummy,a) => tracer('e'),
+                    '*': () => tracer('e'),
                 },
             }),
         },