diff --git a/.eslintrc.json b/.eslintrc.json
index cfe1e0b..9693991 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -1,13 +1,20 @@
 {
     "env": {
-        "browser": true,
-        "es2021": true
+        "node": true,
+        "es2021": true,
+        "jest/globals": true
     },
     "extends": "eslint:recommended",
     "parserOptions": {
         "ecmaVersion": 12,
         "sourceType": "module"
     },
+    "plugins": ["jest"],
     "rules": {
+        "jest/no-disabled-tests": "warn",
+        "jest/no-focused-tests": "error",
+        "jest/no-identical-title": "error",
+        "jest/prefer-to-have-length": "warn",
+        "jest/valid-expect": "error"
     }
 }
diff --git a/cli.js b/cli.js
index a5749bd..987279d 100755
--- a/cli.js
+++ b/cli.js
@@ -1,5 +1,5 @@
 #!/usr/bin/env node
-import { readFileSync, existsSync } from "fs";
+import { readFileSync } from "fs";
 import path from "path";
 import fs from "vinyl-fs";
 import yargs from "yargs";
diff --git a/css.js b/css.js
index 66f2df6..f6fe073 100644
--- a/css.js
+++ b/css.js
@@ -71,7 +71,7 @@ export function rootVariables(rules) {
   if (!root) return {};
   return root.declarations.reduce(
     (obj, { property, value }) =>
-      !/^\-\-/.test(property)
+      !/^--/.test(property)
         ? obj
         : Object.assign(obj, { [property.replace("--", "")]: value }),
     {}
@@ -80,14 +80,14 @@ export function rootVariables(rules) {
 
 function reduceVariables(rules, options = {}) {
   const defaultVariables = rootVariables(rules);
-  const CSS_VAR = /(^var\(\-\-(?<key>.+)\)|(?<val>.+))/;
+  const CSS_VAR = /(^var\(--(?<key>.+)\)|(?<val>.+))/;
   const reduce = (rule) =>
     Object.assign(
       rule,
       rule.declarations
         ? {
             declarations: rule.declarations.map((declaration) => {
-              let { key, val } = CSS_VAR.exec(declaration.value).groups;
+              let key = CSS_VAR.exec(declaration.value).groups.key;
               // only one level of variable referencing is supported
               key =
                 CSS_VAR.exec(options[key] || defaultVariables[key]).groups
diff --git a/css.spec.js b/css.spec.js
index dd43358..64710f3 100644
--- a/css.spec.js
+++ b/css.spec.js
@@ -1,5 +1,3 @@
-import { readFileSync } from "fs";
-import { resolve } from "path";
 import { load, rootVariables, style } from "./css.js";
 
 test("rootVariables", () => {
diff --git a/html.js b/html.js
index 8d1853e..cc034a2 100644
--- a/html.js
+++ b/html.js
@@ -1,4 +1,3 @@
-import fs from "fs";
 import map from "map-stream";
 import escape from "escape-html";
 import * as CSS from "./css.js";
@@ -32,6 +31,7 @@ ${body(tokens, options)}
 }
 
 export function block(
+  // eslint-disable-next-line no-unused-vars
   { text, href, title, pre, alt, h1, h2, h3, li, quote },
   options = {}
 ) {
@@ -63,6 +63,7 @@ export function block(
   }
   if (href) {
     const matchesExt = (url, exts) =>
+      // eslint-disable-next-line no-useless-escape
       exts.some((ext) => new RegExp(`\.${ext}$`).test(url));
 
     if (options.image && matchesExt(href, options.image)) {
diff --git a/package-lock.json b/package-lock.json
index 2618750..242fe65 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -20,6 +20,7 @@
       },
       "devDependencies": {
         "eslint": "^7.23.0",
+        "eslint-plugin-jest": "^24.3.2",
         "jest": "^26.6.3",
         "prettier": "^2.2.1"
       }
@@ -771,6 +772,41 @@
         "node": ">= 10.14.2"
       }
     },
+    "node_modules/@nodelib/fs.scandir": {
+      "version": "2.1.4",
+      "resolved": "https://registry.npmjs.org/@nodelib/fs.scandir/-/fs.scandir-2.1.4.tgz",
+      "integrity": "sha512-33g3pMJk3bg5nXbL/+CY6I2eJDzZAni49PfJnL5fghPTggPvBd/pFNSgJsdAgWptuFu7qq/ERvOYFlhvsLTCKA==",
+      "dev": true,
+      "dependencies": {
+        "@nodelib/fs.stat": "2.0.4",
+        "run-parallel": "^1.1.9"
+      },
+      "engines": {
+        "node": ">= 8"
+      }
+    },
+    "node_modules/@nodelib/fs.stat": {
+      "version": "2.0.4",
+      "resolved": "https://registry.npmjs.org/@nodelib/fs.stat/-/fs.stat-2.0.4.tgz",
+      "integrity": "sha512-IYlHJA0clt2+Vg7bccq+TzRdJvv19c2INqBSsoOLp1je7xjtr7J26+WXR72MCdvU9q1qTzIWDfhMf+DRvQJK4Q==",
+      "dev": true,
+      "engines": {
+        "node": ">= 8"
+      }
+    },
+    "node_modules/@nodelib/fs.walk": {
+      "version": "1.2.6",
+      "resolved": "https://registry.npmjs.org/@nodelib/fs.walk/-/fs.walk-1.2.6.tgz",
+      "integrity": "sha512-8Broas6vTtW4GIXTAHDoE32hnN2M5ykgCpWGbuXHQ15vEMqr23pB76e/GZcYsZCHALv50ktd24qhEyKr6wBtow==",
+      "dev": true,
+      "dependencies": {
+        "@nodelib/fs.scandir": "2.1.4",
+        "fastq": "^1.6.0"
+      },
+      "engines": {
+        "node": ">= 8"
+      }
+    },
     "node_modules/@sinonjs/commons": {
       "version": "1.8.2",
       "resolved": "https://registry.npmjs.org/@sinonjs/commons/-/commons-1.8.2.tgz",
@@ -863,6 +899,12 @@
         "@types/istanbul-lib-report": "*"
       }
     },
+    "node_modules/@types/json-schema": {
+      "version": "7.0.7",
+      "resolved": "https://registry.npmjs.org/@types/json-schema/-/json-schema-7.0.7.tgz",
+      "integrity": "sha512-cxWFQVseBm6O9Gbw1IWb8r6OS4OhSt3hPZLkFApLjM8TEXROBuQGLAH2i2gZpcXdLBIrpXuTDhH7Vbm1iXmNGA==",
+      "dev": true
+    },
     "node_modules/@types/node": {
       "version": "14.14.31",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-14.14.31.tgz",
@@ -902,6 +944,131 @@
       "integrity": "sha512-37RSHht+gzzgYeobbG+KWryeAW8J33Nhr69cjTqSYymXVZEN9NbRYWoYlRtDhHKPVT1FyNKwaTPC1NynKZpzRA==",
       "dev": true
     },
+    "node_modules/@typescript-eslint/experimental-utils": {
+      "version": "4.19.0",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/experimental-utils/-/experimental-utils-4.19.0.tgz",
+      "integrity": "sha512-9/23F1nnyzbHKuoTqFN1iXwN3bvOm/PRIXSBR3qFAYotK/0LveEOHr5JT1WZSzcD6BESl8kPOG3OoDRKO84bHA==",
+      "dev": true,
+      "dependencies": {
+        "@types/json-schema": "^7.0.3",
+        "@typescript-eslint/scope-manager": "4.19.0",
+        "@typescript-eslint/types": "4.19.0",
+        "@typescript-eslint/typescript-estree": "4.19.0",
+        "eslint-scope": "^5.0.0",
+        "eslint-utils": "^2.0.0"
+      },
+      "engines": {
+        "node": "^10.12.0 || >=12.0.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/typescript-eslint"
+      },
+      "peerDependencies": {
+        "eslint": "*"
+      }
+    },
+    "node_modules/@typescript-eslint/scope-manager": {
+      "version": "4.19.0",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/scope-manager/-/scope-manager-4.19.0.tgz",
+      "integrity": "sha512-GGy4Ba/hLXwJXygkXqMzduqOMc+Na6LrJTZXJWVhRrSuZeXmu8TAnniQVKgj8uTRKe4igO2ysYzH+Np879G75g==",
+      "dev": true,
+      "dependencies": {
+        "@typescript-eslint/types": "4.19.0",
+        "@typescript-eslint/visitor-keys": "4.19.0"
+      },
+      "engines": {
+        "node": "^8.10.0 || ^10.13.0 || >=11.10.1"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/typescript-eslint"
+      }
+    },
+    "node_modules/@typescript-eslint/types": {
+      "version": "4.19.0",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/types/-/types-4.19.0.tgz",
+      "integrity": "sha512-A4iAlexVvd4IBsSTNxdvdepW0D4uR/fwxDrKUa+iEY9UWvGREu2ZyB8ylTENM1SH8F7bVC9ac9+si3LWNxcBuA==",
+      "dev": true,
+      "engines": {
+        "node": "^8.10.0 || ^10.13.0 || >=11.10.1"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/typescript-eslint"
+      }
+    },
+    "node_modules/@typescript-eslint/typescript-estree": {
+      "version": "4.19.0",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-4.19.0.tgz",
+      "integrity": "sha512-3xqArJ/A62smaQYRv2ZFyTA+XxGGWmlDYrsfZG68zJeNbeqRScnhf81rUVa6QG4UgzHnXw5VnMT5cg75dQGDkA==",
+      "dev": true,
+      "dependencies": {
+        "@typescript-eslint/types": "4.19.0",
+        "@typescript-eslint/visitor-keys": "4.19.0",
+        "debug": "^4.1.1",
+        "globby": "^11.0.1",
+        "is-glob": "^4.0.1",
+        "semver": "^7.3.2",
+        "tsutils": "^3.17.1"
+      },
+      "engines": {
+        "node": "^10.12.0 || >=12.0.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/typescript-eslint"
+      },
+      "peerDependenciesMeta": {
+        "typescript": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/@typescript-eslint/typescript-estree/node_modules/is-glob": {
+      "version": "4.0.1",
+      "resolved": "https://registry.npmjs.org/is-glob/-/is-glob-4.0.1.tgz",
+      "integrity": "sha512-5G0tKtBTFImOqDnLB2hG6Bp2qcKEFduo4tZu9MT/H6NQv/ghhy30o55ufafxJ/LdH79LLs2Kfrn85TLKyA7BUg==",
+      "dev": true,
+      "dependencies": {
+        "is-extglob": "^2.1.1"
+      },
+      "engines": {
+        "node": ">=0.10.0"
+      }
+    },
+    "node_modules/@typescript-eslint/typescript-estree/node_modules/semver": {
+      "version": "7.3.5",
+      "resolved": "https://registry.npmjs.org/semver/-/semver-7.3.5.tgz",
+      "integrity": "sha512-PoeGJYh8HK4BTO/a9Tf6ZG3veo/A7ZVsYrSA6J8ny9nb3B1VrpkuN+z9OE5wfE5p6H4LchYZsegiQgbJD94ZFQ==",
+      "dev": true,
+      "dependencies": {
+        "lru-cache": "^6.0.0"
+      },
+      "bin": {
+        "semver": "bin/semver.js"
+      },
+      "engines": {
+        "node": ">=10"
+      }
+    },
+    "node_modules/@typescript-eslint/visitor-keys": {
+      "version": "4.19.0",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/visitor-keys/-/visitor-keys-4.19.0.tgz",
+      "integrity": "sha512-aGPS6kz//j7XLSlgpzU2SeTqHPsmRYxFztj2vPuMMFJXZudpRSehE3WCV+BaxwZFvfAqMoSd86TEuM0PQ59E/A==",
+      "dev": true,
+      "dependencies": {
+        "@typescript-eslint/types": "4.19.0",
+        "eslint-visitor-keys": "^2.0.0"
+      },
+      "engines": {
+        "node": "^8.10.0 || ^10.13.0 || >=11.10.1"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/typescript-eslint"
+      }
+    },
     "node_modules/abab": {
       "version": "2.0.5",
       "resolved": "https://registry.npmjs.org/abab/-/abab-2.0.5.tgz",
@@ -1078,6 +1245,15 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/array-union": {
+      "version": "2.1.0",
+      "resolved": "https://registry.npmjs.org/array-union/-/array-union-2.1.0.tgz",
+      "integrity": "sha512-HGyxoOTYUyCM6stUe6EJgnd4EoewAI7zMdfqO+kGjnlZmBDz/cR5pf8r/cR4Wq60sL/p0IkcjUEEPwS3GFrIyw==",
+      "dev": true,
+      "engines": {
+        "node": ">=8"
+      }
+    },
     "node_modules/array-unique": {
       "version": "0.3.2",
       "resolved": "https://registry.npmjs.org/array-unique/-/array-unique-0.3.2.tgz",
@@ -1882,6 +2058,18 @@
         "node": ">= 10.14.2"
       }
     },
+    "node_modules/dir-glob": {
+      "version": "3.0.1",
+      "resolved": "https://registry.npmjs.org/dir-glob/-/dir-glob-3.0.1.tgz",
+      "integrity": "sha512-WkrWp9GR4KXfKGYzOLmTuGVi1UWFfws377n9cc55/tb6DuqyF6pcQ5AbiHEshaDpY9v6oaSr2XCDidGmMwdzIA==",
+      "dev": true,
+      "dependencies": {
+        "path-type": "^4.0.0"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    },
     "node_modules/doctrine": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/doctrine/-/doctrine-3.0.0.tgz",
@@ -2081,6 +2269,27 @@
         "url": "https://opencollective.com/eslint"
       }
     },
+    "node_modules/eslint-plugin-jest": {
+      "version": "24.3.2",
+      "resolved": "https://registry.npmjs.org/eslint-plugin-jest/-/eslint-plugin-jest-24.3.2.tgz",
+      "integrity": "sha512-cicWDr+RvTAOKS3Q/k03+Z3odt3VCiWamNUHWd6QWbVQWcYJyYgUTu8x0mx9GfeDEimawU5kQC+nQ3MFxIM6bw==",
+      "dev": true,
+      "dependencies": {
+        "@typescript-eslint/experimental-utils": "^4.0.1"
+      },
+      "engines": {
+        "node": ">=10"
+      },
+      "peerDependencies": {
+        "@typescript-eslint/eslint-plugin": ">= 4",
+        "eslint": ">=5"
+      },
+      "peerDependenciesMeta": {
+        "@typescript-eslint/eslint-plugin": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/eslint-scope": {
       "version": "5.1.1",
       "resolved": "https://registry.npmjs.org/eslint-scope/-/eslint-scope-5.1.1.tgz",
@@ -2641,6 +2850,47 @@
       "integrity": "sha512-f3qQ9oQy9j2AhBe/H9VC91wLmKBCCU/gDOnKNAYG5hswO7BLKj09Hc5HYNz9cGI++xlpDCIgDaitVs03ATR84Q==",
       "dev": true
     },
+    "node_modules/fast-glob": {
+      "version": "3.2.5",
+      "resolved": "https://registry.npmjs.org/fast-glob/-/fast-glob-3.2.5.tgz",
+      "integrity": "sha512-2DtFcgT68wiTTiwZ2hNdJfcHNke9XOfnwmBRWXhmeKM8rF0TGwmC/Qto3S7RoZKp5cilZbxzO5iTNTQsJ+EeDg==",
+      "dev": true,
+      "dependencies": {
+        "@nodelib/fs.stat": "^2.0.2",
+        "@nodelib/fs.walk": "^1.2.3",
+        "glob-parent": "^5.1.0",
+        "merge2": "^1.3.0",
+        "micromatch": "^4.0.2",
+        "picomatch": "^2.2.1"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    },
+    "node_modules/fast-glob/node_modules/glob-parent": {
+      "version": "5.1.2",
+      "resolved": "https://registry.npmjs.org/glob-parent/-/glob-parent-5.1.2.tgz",
+      "integrity": "sha512-AOIgSQCepiJYwP3ARnGx+5VnTu2HBYdzbGP45eLw1vr3zB3vZLeyed1sC9hnbcOc9/SrMyM5RPQrkGz4aS9Zow==",
+      "dev": true,
+      "dependencies": {
+        "is-glob": "^4.0.1"
+      },
+      "engines": {
+        "node": ">= 6"
+      }
+    },
+    "node_modules/fast-glob/node_modules/is-glob": {
+      "version": "4.0.1",
+      "resolved": "https://registry.npmjs.org/is-glob/-/is-glob-4.0.1.tgz",
+      "integrity": "sha512-5G0tKtBTFImOqDnLB2hG6Bp2qcKEFduo4tZu9MT/H6NQv/ghhy30o55ufafxJ/LdH79LLs2Kfrn85TLKyA7BUg==",
+      "dev": true,
+      "dependencies": {
+        "is-extglob": "^2.1.1"
+      },
+      "engines": {
+        "node": ">=0.10.0"
+      }
+    },
     "node_modules/fast-json-stable-stringify": {
       "version": "2.1.0",
       "resolved": "https://registry.npmjs.org/fast-json-stable-stringify/-/fast-json-stable-stringify-2.1.0.tgz",
@@ -2653,6 +2903,15 @@
       "integrity": "sha1-PYpcZog6FqMMqGQ+hR8Zuqd5eRc=",
       "dev": true
     },
+    "node_modules/fastq": {
+      "version": "1.11.0",
+      "resolved": "https://registry.npmjs.org/fastq/-/fastq-1.11.0.tgz",
+      "integrity": "sha512-7Eczs8gIPDrVzT+EksYBcupqMyxSHXXrHOLRRxU2/DicV8789MRBRR8+Hc2uWzUupOs4YS4JzBmBxjjCVBxD/g==",
+      "dev": true,
+      "dependencies": {
+        "reusify": "^1.0.4"
+      }
+    },
     "node_modules/fb-watchman": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/fb-watchman/-/fb-watchman-2.0.1.tgz",
@@ -2942,6 +3201,35 @@
         "node": ">=4"
       }
     },
+    "node_modules/globby": {
+      "version": "11.0.3",
+      "resolved": "https://registry.npmjs.org/globby/-/globby-11.0.3.tgz",
+      "integrity": "sha512-ffdmosjA807y7+lA1NM0jELARVmYul/715xiILEjo3hBLPTcirgQNnXECn5g3mtR8TOLCVbkfua1Hpen25/Xcg==",
+      "dev": true,
+      "dependencies": {
+        "array-union": "^2.1.0",
+        "dir-glob": "^3.0.1",
+        "fast-glob": "^3.1.1",
+        "ignore": "^5.1.4",
+        "merge2": "^1.3.0",
+        "slash": "^3.0.0"
+      },
+      "engines": {
+        "node": ">=10"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/sindresorhus"
+      }
+    },
+    "node_modules/globby/node_modules/ignore": {
+      "version": "5.1.8",
+      "resolved": "https://registry.npmjs.org/ignore/-/ignore-5.1.8.tgz",
+      "integrity": "sha512-BMpfD7PpiETpBl/A6S498BaIJ6Y/ABT93ETbby2fP00v4EbvPBXWEoaR1UBPKs3iR53pJY7EtZk5KACI57i1Uw==",
+      "dev": true,
+      "engines": {
+        "node": ">= 4"
+      }
+    },
     "node_modules/graceful-fs": {
       "version": "4.2.4",
       "resolved": "https://registry.npmjs.org/graceful-fs/-/graceful-fs-4.2.4.tgz",
@@ -4685,6 +4973,15 @@
       "integrity": "sha512-abv/qOcuPfk3URPfDzmZU1LKmuw8kT+0nIHvKrKgFrwifol/doWcdA4ZqsWQ8ENrFKkd67Mfpo/LovbIUsbt3w==",
       "dev": true
     },
+    "node_modules/merge2": {
+      "version": "1.4.1",
+      "resolved": "https://registry.npmjs.org/merge2/-/merge2-1.4.1.tgz",
+      "integrity": "sha512-8q7VEgMJW4J8tcfVPy8g09NcQwZdbwFEqhe/WZkoIzjn/3TGDwtOCYtXGxA3O8tPzpczCCDgv+P2P5y00ZJOOg==",
+      "dev": true,
+      "engines": {
+        "node": ">= 8"
+      }
+    },
     "node_modules/micromatch": {
       "version": "4.0.2",
       "resolved": "https://registry.npmjs.org/micromatch/-/micromatch-4.0.2.tgz",
@@ -5207,6 +5504,15 @@
       "integrity": "sha512-GSmOT2EbHrINBf9SR7CDELwlJ8AENk3Qn7OikK4nFYAu3Ote2+JYNVvkpAEQm3/TLNEJFD/xZJjzyxg3KBWOzw==",
       "dev": true
     },
+    "node_modules/path-type": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/path-type/-/path-type-4.0.0.tgz",
+      "integrity": "sha512-gDKb8aZMDeD/tZWs9P6+q0J9Mwkdl6xMV8TjnGP3qJVJ06bdMgkbBlLU8IdfOsIsFz2BW1rNVT3XuNEl8zPAvw==",
+      "dev": true,
+      "engines": {
+        "node": ">=8"
+      }
+    },
     "node_modules/performance-now": {
       "version": "2.1.0",
       "resolved": "https://registry.npmjs.org/performance-now/-/performance-now-2.1.0.tgz",
@@ -5361,6 +5667,26 @@
         "node": ">=0.6"
       }
     },
+    "node_modules/queue-microtask": {
+      "version": "1.2.3",
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+      "resolved": "https://registry.npmjs.org/reusify/-/reusify-1.0.4.tgz",
+      "integrity": "sha512-U9nH88a3fc/ekCF1l0/UP1IosiuIjyTh7hBvXVMHYgVcfGvt897Xguj2UOLDeI5BG2m7/uwyaLVT6fbtCwTyzw==",
+      "dev": true
+    },
     "rimraf": {
       "version": "3.0.2",
       "resolved": "https://registry.npmjs.org/rimraf/-/rimraf-3.0.2.tgz",
@@ -11768,6 +12382,15 @@
       "integrity": "sha512-nfMOlASu9OnRJo1mbEk2cz0D56a1MBNrJ7orjRZQG10XDyuvwksKbuXNp6qa+kbn839HwjwhBzhFmdsaEAfauA==",
       "dev": true
     },
+    "run-parallel": {
+      "version": "1.2.0",
+      "resolved": "https://registry.npmjs.org/run-parallel/-/run-parallel-1.2.0.tgz",
+      "integrity": "sha512-5l4VyZR86LZ/lDxZTR6jqL8AFE2S0IFLMP26AbjsLVADxHdhB/c0GUsH+y39UfCi3dzz8OlQuPmnaJOMoDHQBA==",
+      "dev": true,
+      "requires": {
+        "queue-microtask": "^1.2.2"
+      }
+    },
     "safe-buffer": {
       "version": "5.1.2",
       "resolved": "https://registry.npmjs.org/safe-buffer/-/safe-buffer-5.1.2.tgz",
@@ -12557,6 +13180,21 @@
         "punycode": "^2.1.1"
       }
     },
+    "tslib": {
+      "version": "1.14.1",
+      "resolved": "https://registry.npmjs.org/tslib/-/tslib-1.14.1.tgz",
+      "integrity": "sha512-Xni35NKzjgMrwevysHTCArtLDpPvye8zV/0E4EyYn43P7/7qvQwPh9BGkHewbMulVntbigmcT7rdX3BNo9wRJg==",
+      "dev": true
+    },
+    "tsutils": {
+      "version": "3.21.0",
+      "resolved": "https://registry.npmjs.org/tsutils/-/tsutils-3.21.0.tgz",
+      "integrity": "sha512-mHKK3iUXL+3UF6xL5k0PEhKRUBKPBCv/+RkEOpjRWxxx27KKRBmmA60A9pgOUvMi8GKhRMPEmjBRPzs2W7O1OA==",
+      "dev": true,
+      "requires": {
+        "tslib": "^1.8.1"
+      }
+    },
     "tunnel-agent": {
       "version": "0.6.0",
       "resolved": "https://registry.npmjs.org/tunnel-agent/-/tunnel-agent-0.6.0.tgz",
@@ -12602,6 +13240,13 @@
         "is-typedarray": "^1.0.0"
       }
     },
+    "typescript": {
+      "version": "4.2.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-4.2.3.tgz",
+      "integrity": "sha512-qOcYwxaByStAWrBf4x0fibwZvMRG+r4cQoTjbPtUlrWjBHbmCAww1i448U0GJ+3cNNEtebDteo/cHOR3xJ4wEw==",
+      "dev": true,
+      "peer": true
+    },
     "unc-path-regex": {
       "version": "0.1.2",
       "resolved": "https://registry.npmjs.org/unc-path-regex/-/unc-path-regex-0.1.2.tgz",
diff --git a/package.json b/package.json
index ef8d69e..9b4d68e 100644
--- a/package.json
+++ b/package.json
@@ -25,6 +25,7 @@
     "UNLICENSE"
   ],
   "scripts": {
+    "lint": "eslint .",
     "test": "NODE_OPTIONS=--experimental-vm-modules jest",
     "test:watch": "NODE_OPTIONS=--experimental-vm-modules jest --watch",
     "test:update": "NODE_OPTIONS=--experimental-vm-modules jest --updateSnapshot",
@@ -39,6 +40,7 @@
   },
   "devDependencies": {
     "eslint": "^7.23.0",
+    "eslint-plugin-jest": "^24.3.2",
     "jest": "^26.6.3",
     "prettier": "^2.2.1"
   },