diff --git a/.eslintrc.cjs b/.eslintrc.cjs
index 2802a161..a0729fae 100644
--- a/.eslintrc.cjs
+++ b/.eslintrc.cjs
@@ -29,5 +29,13 @@ module.exports = {
                 "@typescript-eslint/no-var-requires": "off",
             },
         },
+        {
+            files: ["./spec/**/*"],
+            env: {
+                browser: false,
+            },
+            extends: ["plugin:jest/recommended"],
+            plugins: ["jest"],
+        },
     ],
 };
diff --git a/jest.config.js b/jest.config.js
index 3e74f815..7d3bde02 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -2,11 +2,15 @@
 //
 // SPDX-License-Identifier: MIT
 
-export default {
+/** @type {import('ts-jest/dist/types').InitialOptionsTsJest} */
+const config = {
     preset: "ts-jest",
     globals: {
         "ts-jest": {
-            tsconfig: "<rootDir>/spec/tsconfig.spec.json",
+            tsconfig: "<rootDir>/spec/tsconfig.json",
         },
     },
+    setupFiles: ["<rootDir>/spec/setup.ts"],
 };
+
+export default config;
diff --git a/spec/localization/localization.spec.ts b/spec/localization/localization.spec.ts
index 4c62e45a..a050cf71 100644
--- a/spec/localization/localization.spec.ts
+++ b/spec/localization/localization.spec.ts
@@ -2,14 +2,10 @@
 //
 // SPDX-License-Identifier: MIT
 
-import * as fs from "fs-extra";
-import * as path from "path";
+import en from "../../lang/en.json";
+import de from "../../lang/de.json";
 
 describe("English and german localization files", () => {
-    const localizationPath = "./lang/";
-    const en: Record<string, unknown> = fs.readJSONSync(path.join(localizationPath, "en.json"));
-    const de: Record<string, unknown> = fs.readJSONSync(path.join(localizationPath, "de.json"));
-
     it("should have the same keys.", () => {
         const deKeys = Object.keys(de);
         const enKeys = Object.keys(en);
diff --git a/spec/rolls/check-evaluation.spec.ts b/spec/rolls/check-evaluation.spec.ts
index bde1ddbf..5e5e954c 100644
--- a/spec/rolls/check-evaluation.spec.ts
+++ b/spec/rolls/check-evaluation.spec.ts
@@ -5,39 +5,21 @@
 
 import evaluateCheck from "../../src/rolls/check-evaluation";
 
-class StubGame {
-    constructor() {
-        this.i18n = {
-            localize: (key: string) => key,
-        };
-    }
-    i18n: {
-        localize: (key: string) => string;
-    };
-}
-
-const game = new StubGame();
-
-Object.defineProperties(globalThis, {
-    game: { value: game },
-    Game: { value: StubGame },
-});
-
 describe("evaluateCheck with no dice", () => {
     it("should throw an error.", () => {
-        expect(() => evaluateCheck([], 10)).toThrow("DS4.ErrorInvalidNumberOfDice");
+        expect(() => evaluateCheck([], 10)).toThrow("Invalid number of dice.");
     });
 });
 
 describe("evaluateCheck with more dice than required by the checkTargetNumber", () => {
     it("should throw an error.", () => {
-        expect(() => evaluateCheck([10, 10], 10)).toThrow("DS4.ErrorInvalidNumberOfDice");
+        expect(() => evaluateCheck([10, 10], 10)).toThrow("Invalid number of dice.");
     });
 });
 
 describe("evaluateCheck with less dice than required by the checkTargetNumber", () => {
     it("should throw an error.", () => {
-        expect(() => evaluateCheck([10], 21)).toThrow("DS4.ErrorInvalidNumberOfDice");
+        expect(() => evaluateCheck([10], 21)).toThrow("Invalid number of dice.");
     });
 });
 
diff --git a/spec/setup.ts b/spec/setup.ts
new file mode 100644
index 00000000..9b10aba6
--- /dev/null
+++ b/spec/setup.ts
@@ -0,0 +1,27 @@
+// SPDX-FileCopyrightText: 2022 Johannes Loher
+//
+// SPDX-License-Identifier: MIT
+
+import en from "../lang/en.json";
+
+function setupStubs() {
+    class StubGame {
+        constructor() {
+            this.i18n = {
+                localize: (key: string) => (key in en ? en[key as keyof typeof en] : key),
+            };
+        }
+        i18n: {
+            localize: (key: string) => string;
+        };
+    }
+
+    const game = new StubGame();
+
+    Object.defineProperties(globalThis, {
+        game: { value: game },
+        Game: { value: StubGame },
+    });
+}
+
+setupStubs();
diff --git a/spec/tsconfig.spec.json b/spec/tsconfig.json
similarity index 100%
rename from spec/tsconfig.spec.json
rename to spec/tsconfig.json
diff --git a/spec/tsconfig.spec.json.license b/spec/tsconfig.json.license
similarity index 100%
rename from spec/tsconfig.spec.json.license
rename to spec/tsconfig.json.license
diff --git a/tsconfig.json b/tsconfig.json
index b8fbff11..7a7a51ce 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -7,7 +7,8 @@
         "moduleResolution": "node",
         "forceConsistentCasingInFileNames": true,
         "strict": true,
-        "noUncheckedIndexedAccess": true
+        "noUncheckedIndexedAccess": true,
+        "resolveJsonModule": true
     },
     "include": ["src"]
 }