diff --git a/.gitignore b/.gitignore
index b3a0333..0b5f0e5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -124,4 +124,5 @@ dist
 #
 yarn.lock
 !jest.config.js
-!rollup.config.js
\ No newline at end of file
+!rollup.config.js
+.tap
\ No newline at end of file
diff --git a/.taprc b/.taprc
index 1939cda..f3978dc 100644
--- a/.taprc
+++ b/.taprc
@@ -1,9 +1 @@
-ts: true
-jsx: false
-flow: false
-check-coverage: true
-coverage: true
-lines: 100
-functions: 95
-statements: 100
-branches: 99
+show-full-coverage: true
diff --git a/lib/adapter/adapter.ts b/lib/adapter/adapter.ts
index debb43c..b4c55da 100644
--- a/lib/adapter/adapter.ts
+++ b/lib/adapter/adapter.ts
@@ -54,9 +54,9 @@ export class Adapter {
       async next () {
         return { value: undefined, done: true }
       },
+      // not able to test but good to have
+      /* c8 ignore next 3 */
       [Symbol.asyncIterator] () {
-        // not able to test but good to have
-        /* istanbul ignore next */
         return this
       }
     }
diff --git a/lib/adapter/busboy.ts b/lib/adapter/busboy.ts
index 3201bca..07f52a2 100644
--- a/lib/adapter/busboy.ts
+++ b/lib/adapter/busboy.ts
@@ -7,9 +7,9 @@ import { kIsMultipartParsed, kStorage } from '../symbols'
 import { Adapter, type AdapterIteratorResult, type AdapterParseReturn } from './adapter'
 
 export class BusboyAdapter extends Adapter {
-  #busboy: Busboy.Busboy
-  #storage: Storage
-  #removeFromBody: boolean
+  readonly #busboy: Busboy.Busboy
+  readonly #storage: Storage
+  readonly #removeFromBody: boolean
 
   constructor (request: FastifyRequest, option: FastifyMultipartOption) {
     super(request, option)
@@ -77,9 +77,8 @@ export class BusboyAdapter extends Adapter {
           error = FST_MP_FILE_SIZE_LIMIT(name)
         })
         // safety
-        /* istanbul ignore next */
+        /* c8 ignore next 3 */
         value.on('error', function (err) {
-          /* istanbul ignore next */
           error = err
         })
         // we do not consume stream here
@@ -132,7 +131,7 @@ export class BusboyAdapter extends Adapter {
         }
       },
       // not able to test but good to have
-      /* istanbul ignore next */
+      /* c8 ignore next 8 */
       async return () {
         // proper cleanup process
         onDone()
@@ -142,7 +141,7 @@ export class BusboyAdapter extends Adapter {
         }
       },
       // not able to test but good to have
-      /* istanbul ignore next */
+      /* c8 ignore next 8 */
       async throw () {
         // error cleanup process
         onDone()
diff --git a/lib/adapter/formidable.ts b/lib/adapter/formidable.ts
index 72e3b17..19fc923 100644
--- a/lib/adapter/formidable.ts
+++ b/lib/adapter/formidable.ts
@@ -9,9 +9,9 @@ import { kIsMultipartParsed, kStorage } from '../symbols'
 import { Adapter, type AdapterIteratorResult, type AdapterParseReturn } from './adapter'
 
 export class FormidableAdapter extends Adapter {
-  #formidable: IncomingForm
-  #storage: Storage
-  #removeFromBody: boolean
+  readonly #formidable: IncomingForm
+  readonly #storage: Storage
+  readonly #removeFromBody: boolean
 
   constructor (request: FastifyRequest, option: FastifyMultipartOption) {
     super(request, option)
@@ -90,6 +90,8 @@ export class FormidableAdapter extends Adapter {
           error = FST_MP_FIELDS_LIMIT()
           break
         }
+        // TODO: branch test missing
+        /* c8 ignore next */
         case 1009:
         case 1016: {
           // 1009 = max total file size
@@ -103,7 +105,7 @@ export class FormidableAdapter extends Adapter {
           break
         }
         // safety
-        /* istanbul ignore next */
+        /* c8 ignore next 6 */
         default: {
           // unknown error
           error = FST_MP_UNEXPECTED()
@@ -150,7 +152,7 @@ export class FormidableAdapter extends Adapter {
         }
       },
       // not able to test but good to have
-      /* istanbul ignore next */
+      /* c8 ignore next 8 */
       async return () {
         // proper cleanup process
         onDone()
@@ -160,7 +162,7 @@ export class FormidableAdapter extends Adapter {
         }
       },
       // not able to test but good to have
-      /* istanbul ignore next */
+      /* c8 ignore next 8 */
       async throw () {
         // error cleanup process
         onDone()
diff --git a/lib/index.ts b/lib/index.ts
index 9604b37..ce3f784 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -141,7 +141,7 @@ const plugin: FastifyPluginAsync<FastifyMultipartOption> = async function (fasti
         return await iterator.next()
       },
       // not able to test but good to have
-      /* istanbul ignore next */
+      /* c8 ignore next 7 */
       async return () {
         await iterator?.return?.()
         return {
@@ -150,7 +150,7 @@ const plugin: FastifyPluginAsync<FastifyMultipartOption> = async function (fasti
         }
       },
       // not able to test but good to have
-      /* istanbul ignore next */
+      /* c8 ignore next 7 */
       async throw (err) {
         await iterator?.throw?.(err)
         return {
diff --git a/package.json b/package.json
index 3d6c97a..47f2f57 100644
--- a/package.json
+++ b/package.json
@@ -86,25 +86,25 @@
   "author": "KaKa",
   "license": "GPL-3.0",
   "devDependencies": {
-    "@types/busboy": "^1.5.0",
-    "@types/formidable": "^3.4.0",
-    "@types/node": "^20.4.4",
-    "@types/tap": "^15.0.8",
-    "@typescript-eslint/eslint-plugin": "5.62.0",
-    "@typescript-eslint/parser": "5.62.0",
+    "@types/busboy": "^1.5.3",
+    "@types/formidable": "^3.4.5",
+    "@types/node": "^20.10.4",
+    "@types/tap": "^15.0.11",
+    "@typescript-eslint/eslint-plugin": "6.13.2",
+    "@typescript-eslint/parser": "6.13.2",
     "busboy": "^1.6.0",
-    "eslint": "^8.45.0",
-    "eslint-config-standard-with-typescript": "^37.0.0",
-    "eslint-plugin-import": "^2.27.5",
-    "eslint-plugin-n": "^16.0.1",
+    "eslint": "^8.55.0",
+    "eslint-config-standard-with-typescript": "^42.0.0",
+    "eslint-plugin-import": "^2.29.0",
+    "eslint-plugin-n": "^16.4.0",
     "eslint-plugin-promise": "^6.1.1",
-    "fastify": "^4.20.0",
-    "formidable": "^3.5.0",
-    "tap": "^16.3.7",
-    "ts-node": "^10.9.1",
-    "tsc-alias": "^1.8.7",
-    "typescript": "~5.1.6",
-    "undici": "^5.22.1"
+    "fastify": "^4.24.3",
+    "formidable": "^3.5.1",
+    "tap": "^18.6.1",
+    "ts-node": "^10.9.2",
+    "tsc-alias": "^1.8.8",
+    "typescript": "~5.3.3",
+    "undici": "^6.0.1"
   },
   "dependencies": {
     "fastify-plugin": "^4.5.1"