diff --git a/package-lock.json b/package-lock.json
index b6d2b42..992d230 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,6 +11,8 @@
       "devDependencies": {
         "@rollup/plugin-node-resolve": "^14.1.0",
         "@types/mocha": "^10.0.1",
+        "@types/sinon": "^17.0.3",
+        "@types/sinon-chai": "^3.2.12",
         "chai": "^4.3.4",
         "cpx": "^1.5.0",
         "eslint": "^8.28.0",
@@ -324,6 +326,12 @@
       "integrity": "sha512-sXXKG+uL9IrKqViTtao2Ws6dy0znu9sOaP1di/jKGW1M6VssO8vlpXCQcpZ+jisQ1tTFAC5Jo/EOzFbggBagFQ==",
       "dev": true
     },
+    "node_modules/@types/chai": {
+      "version": "4.3.11",
+      "resolved": "https://registry.npmjs.org/@types/chai/-/chai-4.3.11.tgz",
+      "integrity": "sha512-qQR1dr2rGIHYlJulmr8Ioq3De0Le9E4MJ5AiaeAETJJpndT1uUNHsGFK3L/UIu+rbkQSdj8J/w2bCsBZc/Y5fQ==",
+      "dev": true
+    },
     "node_modules/@types/estree": {
       "version": "0.0.39",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-0.0.39.tgz",
@@ -351,6 +359,31 @@
         "@types/node": "*"
       }
     },
+    "node_modules/@types/sinon": {
+      "version": "17.0.3",
+      "resolved": "https://registry.npmjs.org/@types/sinon/-/sinon-17.0.3.tgz",
+      "integrity": "sha512-j3uovdn8ewky9kRBG19bOwaZbexJu/XjtkHyjvUgt4xfPFz18dcORIMqnYh66Fx3Powhcr85NT5+er3+oViapw==",
+      "dev": true,
+      "dependencies": {
+        "@types/sinonjs__fake-timers": "*"
+      }
+    },
+    "node_modules/@types/sinon-chai": {
+      "version": "3.2.12",
+      "resolved": "https://registry.npmjs.org/@types/sinon-chai/-/sinon-chai-3.2.12.tgz",
+      "integrity": "sha512-9y0Gflk3b0+NhQZ/oxGtaAJDvRywCa5sIyaVnounqLvmf93yBF4EgIRspePtkMs3Tr844nCclYMlcCNmLCvjuQ==",
+      "dev": true,
+      "dependencies": {
+        "@types/chai": "*",
+        "@types/sinon": "*"
+      }
+    },
+    "node_modules/@types/sinonjs__fake-timers": {
+      "version": "8.1.5",
+      "resolved": "https://registry.npmjs.org/@types/sinonjs__fake-timers/-/sinonjs__fake-timers-8.1.5.tgz",
+      "integrity": "sha512-mQkU2jY8jJEF7YHjHvsQO8+3ughTL1mcnn96igfhONmR+fUPSKIkefQYpSe8bsly2Ep7oQbn/6VG5/9/0qcArQ==",
+      "dev": true
+    },
     "node_modules/@ungap/promise-all-settled": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/@ungap/promise-all-settled/-/promise-all-settled-1.1.2.tgz",
@@ -6115,6 +6148,12 @@
       "integrity": "sha512-sXXKG+uL9IrKqViTtao2Ws6dy0znu9sOaP1di/jKGW1M6VssO8vlpXCQcpZ+jisQ1tTFAC5Jo/EOzFbggBagFQ==",
       "dev": true
     },
+    "@types/chai": {
+      "version": "4.3.11",
+      "resolved": "https://registry.npmjs.org/@types/chai/-/chai-4.3.11.tgz",
+      "integrity": "sha512-qQR1dr2rGIHYlJulmr8Ioq3De0Le9E4MJ5AiaeAETJJpndT1uUNHsGFK3L/UIu+rbkQSdj8J/w2bCsBZc/Y5fQ==",
+      "dev": true
+    },
     "@types/estree": {
       "version": "0.0.39",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-0.0.39.tgz",
@@ -6142,6 +6181,31 @@
         "@types/node": "*"
       }
     },
+    "@types/sinon": {
+      "version": "17.0.3",
+      "resolved": "https://registry.npmjs.org/@types/sinon/-/sinon-17.0.3.tgz",
+      "integrity": "sha512-j3uovdn8ewky9kRBG19bOwaZbexJu/XjtkHyjvUgt4xfPFz18dcORIMqnYh66Fx3Powhcr85NT5+er3+oViapw==",
+      "dev": true,
+      "requires": {
+        "@types/sinonjs__fake-timers": "*"
+      }
+    },
+    "@types/sinon-chai": {
+      "version": "3.2.12",
+      "resolved": "https://registry.npmjs.org/@types/sinon-chai/-/sinon-chai-3.2.12.tgz",
+      "integrity": "sha512-9y0Gflk3b0+NhQZ/oxGtaAJDvRywCa5sIyaVnounqLvmf93yBF4EgIRspePtkMs3Tr844nCclYMlcCNmLCvjuQ==",
+      "dev": true,
+      "requires": {
+        "@types/chai": "*",
+        "@types/sinon": "*"
+      }
+    },
+    "@types/sinonjs__fake-timers": {
+      "version": "8.1.5",
+      "resolved": "https://registry.npmjs.org/@types/sinonjs__fake-timers/-/sinonjs__fake-timers-8.1.5.tgz",
+      "integrity": "sha512-mQkU2jY8jJEF7YHjHvsQO8+3ughTL1mcnn96igfhONmR+fUPSKIkefQYpSe8bsly2Ep7oQbn/6VG5/9/0qcArQ==",
+      "dev": true
+    },
     "@ungap/promise-all-settled": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/@ungap/promise-all-settled/-/promise-all-settled-1.1.2.tgz",
diff --git a/package.json b/package.json
index f6cf148..932b66f 100644
--- a/package.json
+++ b/package.json
@@ -42,6 +42,8 @@
   "devDependencies": {
     "@rollup/plugin-node-resolve": "^14.1.0",
     "@types/mocha": "^10.0.1",
+    "@types/sinon": "^17.0.3",
+    "@types/sinon-chai": "^3.2.12",
     "chai": "^4.3.4",
     "cpx": "^1.5.0",
     "eslint": "^8.28.0",
diff --git a/test/index.spec.ts b/test/index.spec.ts
new file mode 100644
index 0000000..af78494
--- /dev/null
+++ b/test/index.spec.ts
@@ -0,0 +1,19 @@
+import { expect } from 'chai';
+
+import {
+  flatten
+} from '../lib/index.js';
+
+
+describe('min-dash', function() {
+
+  it('should work', function() {
+
+    // given
+    const arr = [ [ 'A', 'B', 'C' ], 'B' ];
+
+    // when
+    expect(flatten(arr)).to.eql(arr);
+  });
+
+});
\ No newline at end of file
diff --git a/tsconfig.json b/tsconfig.json
index 169a5fe..5849ac0 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,6 +1,7 @@
 {
   "include": [
-    "test/*.js"
+    "test/*.js",
+    "test/*.ts"
   ],
   "compilerOptions": {
     "strict": true,