diff --git a/package.json b/package.json
index 6d6599f..1327c5a 100644
--- a/package.json
+++ b/package.json
@@ -46,6 +46,7 @@
     "puppeteer": ">=8"
   },
   "devDependencies": {
+    "@types/jest": "^26.0.20",
     "@types/mdast": "^3.0.3",
     "@types/mermaid": "^8.2.2",
     "@typescript-eslint/eslint-plugin": "^4.17.0",
diff --git a/yarn.lock b/yarn.lock
index 7604fef..cffb349 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -628,6 +628,14 @@
   dependencies:
     "@types/istanbul-lib-report" "*"
 
+"@types/jest@^26.0.20":
+  version "26.0.20"
+  resolved "https://registry.yarnpkg.com/@types/jest/-/jest-26.0.20.tgz#cd2f2702ecf69e86b586e1f5223a60e454056307"
+  integrity sha512-9zi2Y+5USJRxd0FsahERhBwlcvFh6D2GLQnY2FH2BzK8J9s9omvNHIbvABwIluXa0fD8XVKMLTO0aOEuUfACAA==
+  dependencies:
+    jest-diff "^26.0.0"
+    pretty-format "^26.0.0"
+
 "@types/json-schema@^7.0.3":
   version "7.0.7"
   resolved "https://registry.yarnpkg.com/@types/json-schema/-/json-schema-7.0.7.tgz#98a993516c859eb0d5c4c8f098317a9ea68db9ad"
@@ -3362,7 +3370,7 @@ jest-config@^26.6.3:
     micromatch "^4.0.2"
     pretty-format "^26.6.2"
 
-jest-diff@^26.6.1, jest-diff@^26.6.2:
+jest-diff@^26.0.0, jest-diff@^26.6.1, jest-diff@^26.6.2:
   version "26.6.2"
   resolved "https://registry.yarnpkg.com/jest-diff/-/jest-diff-26.6.2.tgz#1aa7468b52c3a68d7d5c5fdcdfcd5e49bd164394"
   integrity sha512-6m+9Z3Gv9wN0WFVasqjCL/06+EFCMTqDEUl/b87HYK2rAPTyfz4ZIuSlPhY51PIQRWx5TaxeF1qmXKe9gfN3sA==
@@ -4620,7 +4628,7 @@ prettier@^2.2.1:
   resolved "https://registry.yarnpkg.com/prettier/-/prettier-2.2.1.tgz#795a1a78dd52f073da0cd42b21f9c91381923ff5"
   integrity sha512-PqyhM2yCjg/oKkFPtTGUojv7gnZAoG80ttl45O6x2Ug/rMJw4wcc9k6aaf2hibP7BGVCCM33gZoGjyvt9mm16Q==
 
-pretty-format@^26.6.2:
+pretty-format@^26.0.0, pretty-format@^26.6.2:
   version "26.6.2"
   resolved "https://registry.yarnpkg.com/pretty-format/-/pretty-format-26.6.2.tgz#e35c2705f14cb7fe2fe94fa078345b444120fc93"
   integrity sha512-7AeGuCYNGmycyQbCqd/3PWH4eOoX/OiCa0uphp57NVTeAGdJGaAliecxwBDHYQCIvrW7aDBZCYeNTP/WX69mkg==