diff --git a/package.json b/package.json
index 18f336b..b548099 100644
--- a/package.json
+++ b/package.json
@@ -48,7 +48,7 @@
     "jsdom": "^20.0.0",
     "prettier": "^2.5.1",
     "typescript": "^4.7.4",
-    "vitest": "^0.27.3",
+    "vitest": "^0.28.6",
     "vue-tsc": "^0.38.1"
   },
   "engines": {
diff --git a/tests/game/formulas.test.ts b/tests/game/formulas.test.ts
index d9be004..eed9d42 100644
--- a/tests/game/formulas.test.ts
+++ b/tests/game/formulas.test.ts
@@ -11,8 +11,22 @@ import { ref } from "vue";
 
 type FormulaFunctions = keyof GenericFormula & keyof typeof Formula & keyof typeof Decimal;
 
+interface CustomMatchers<R = unknown> {
+    compare_tolerance(expected: DecimalSource): R;
+}
+
+declare global {
+    // eslint-disable-next-line @typescript-eslint/no-namespace
+    namespace Vi {
+        // eslint-disable-next-line @typescript-eslint/no-empty-interface
+        interface Assertion extends CustomMatchers {}
+        // eslint-disable-next-line @typescript-eslint/no-empty-interface
+        interface AsymmetricMatchersContaining extends CustomMatchers {}
+    }
+}
+
 expect.extend({
-    compare_tolerance(received, expected) {
+    compare_tolerance(received: DecimalSource, expected: DecimalSource) {
         const { isNot } = this;
         let pass = false;
         if (!Decimal.isFinite(expected)) {
@@ -35,20 +49,6 @@ expect.extend({
     }
 });
 
-interface CustomMatchers<R = unknown> {
-    compare_tolerance(expected: DecimalSource): R;
-}
-
-declare global {
-    // eslint-disable-next-line @typescript-eslint/no-namespace
-    namespace Vi {
-        // eslint-disable-next-line @typescript-eslint/no-empty-interface
-        interface Assertion extends CustomMatchers {}
-        // eslint-disable-next-line @typescript-eslint/no-empty-interface
-        interface AsymmetricMatchersContaining extends CustomMatchers {}
-    }
-}
-
 const testValues = ["-1e400", 0, 0.25] as const;
 
 const invertibleZeroParamFunctionNames = [
diff --git a/vite.config.ts b/vite.config.ts
index 080d8e6..f3ce360 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -57,8 +57,5 @@ export default defineConfig({
                 ]
             }
         })
-    ],
-    test: {
-        environment: "jsdom"
-    }
+    ]
 });
diff --git a/vitest.config.ts b/vitest.config.ts
new file mode 100644
index 0000000..3ab791b
--- /dev/null
+++ b/vitest.config.ts
@@ -0,0 +1,9 @@
+import { mergeConfig } from 'vite'
+import { defineConfig } from 'vitest/config'
+import viteConfig from './vite.config'
+
+export default mergeConfig(viteConfig, defineConfig({
+    test: {
+        environment: "jsdom"
+    }
+}))