diff --git a/README.md b/README.md
index 4093734..bcc783d 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,7 @@ const warning = createWarning({
   message: 'Hello %s',
   unlimited: true
 })
-warning('world')
+const emitted = warning('world')
 ```
 
 #### Methods
@@ -101,6 +101,45 @@ FST_ERROR_CODE('world') // will be emitted
 FST_ERROR_CODE('world') // will be emitted again
 ```
 
+#### `spyWarning(warning)`
+
+Spy the created warning function for testing purpose.
+
+```js
+const { test } = require('node:test')
+const { createWarning, spyWarning } = require('process-warning')
+const FST_ERROR_CODE = createWarning({ name: 'MyAppWarning', code: 'FST_ERROR_CODE', message: 'Hello %s' })
+
+test('spy warning', t => {
+  const spyData = spyWarning(FST_ERROR_CODE)
+
+  // call after spy
+  const emitted = FST_ERROR_CODE('world')
+  t.assert.strictEqual(emitted, true)
+
+  // restore the warning function
+  // it must be called when you do not need to spy anymore
+  // otherwise, the calls data will accumulates.
+  t.after(() => spyData.restore())
+
+  t.assert.strictEqual(FST_ERROR_CODE.emitted, true)
+  // calls return the arguments and result.
+  // result indicate whether warning is emitted through process.emitWarning
+  console.log(spyData.calls) // [{ arguments: ['world'], result: true }]
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['world'])
+  t.assert.strictEqual(spyData.calls[0].result,  true)
+  // number of times called the function
+  console.log(spyData.callCount()) // 1
+  t.assert.strictEqual(spyData.callCount(),  1)
+
+  // reset the spy stat and warning state
+  spyData.reset()
+  t.assert.strictEqual(FST_ERROR_CODE.emitted, false)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(),  0)
+})
+```
+
 #### Suppressing warnings
 
 It is possible to suppress warnings by utilizing one of node's built-in warning suppression mechanisms.
diff --git a/index.js b/index.js
index e0d4ab8..78455f8 100644
--- a/index.js
+++ b/index.js
@@ -17,6 +17,7 @@ const { format } = require('node:util')
  * @property {string} message - The warning message.
  * @property {boolean} emitted - Indicates if the warning has been emitted.
  * @property {function} format - Formats the warning message.
+ * @returns {boolean} emit - Indicates if the warning has been emitted by this call.
  */
 
 /**
@@ -33,8 +34,69 @@ const { format } = require('node:util')
  * @typedef {Object} ProcessWarning
  * @property {function} createWarning - Creates a warning item.
  * @property {function} createDeprecation - Creates a deprecation warning item.
+ * @property {function} spyWarning - Spy a warning item.
  */
 
+/**
+ * Represents the spy data.
+ * @typedef {Object} WarningSpyData
+ * @property {object} calls - Arguments of WarningItem calls with.
+ * @property {function} callCount - Number of counts called the WarningItem.
+ * @property {function} reset - Reset the calls data and state of WarningItem.
+ * @property {function} restore - Remove spy from WarningItem.
+ */
+
+const kWarningFn = Symbol('process-warning.fn')
+const kWarningSpyData = Symbol('process-warning.spyData')
+
+/**
+ * Spy a warning item.
+ * @function
+ * @memberof processWarning
+ * @param {WarningItem} warning - The warning item to spy.
+ * @returns {WarningSpyData} The created spy data.
+ */
+function spyWarning (warning) {
+  // Do not double spy the same warning
+  if (warning[kWarningSpyData] === null) {
+    const warningFn = warning[kWarningFn]
+    warning[kWarningFn] = function (a, b, c) {
+      const args = []
+      // since warning always call by fn(a, b, c)
+      // it need to remove the trailing undefined arguments
+      if (c) {
+        args.push(a, b, c)
+      } else if (b) {
+        args.push(a, b)
+      } else if (a) {
+        args.push(a)
+      }
+      warning[kWarningSpyData].calls.push({
+        arguments: args,
+        result: warningFn(a, b, c)
+      })
+    }
+    const spyData = {
+      calls: [],
+      callCount () {
+        return spyData.calls.length
+      },
+      reset () {
+        warning.emitted = false
+        spyData.calls.length = 0
+      },
+      restore () {
+        spyData.reset()
+        warning[kWarningFn] = warningFn
+        warning[kWarningSpyData] = null
+      }
+    }
+    warning[kWarningSpyData] = spyData
+  }
+
+  return warning[kWarningSpyData]
+}
+
 /**
  * Creates a deprecation warning item.
  * @function
@@ -62,21 +124,24 @@ function createWarning ({ name, code, message, unlimited = false } = {}) {
 
   code = code.toUpperCase()
 
-  let warningContainer = {
-    [name]: function (a, b, c) {
+  const warningFn = unlimited === true
+    ? function (a, b, c) {
+      warning.emitted = true
+      process.emitWarning(warning.format(a, b, c), warning.name, warning.code)
+      return true
+    }
+    : function (a, b, c) {
       if (warning.emitted === true && warning.unlimited !== true) {
-        return
+        return false
       }
       warning.emitted = true
       process.emitWarning(warning.format(a, b, c), warning.name, warning.code)
+      return true
     }
-  }
-  if (unlimited) {
-    warningContainer = {
-      [name]: function (a, b, c) {
-        warning.emitted = true
-        process.emitWarning(warning.format(a, b, c), warning.name, warning.code)
-      }
+
+  const warningContainer = {
+    [name]: function (a, b, c) {
+      return warning[kWarningFn](a, b, c)
     }
   }
 
@@ -86,14 +151,16 @@ function createWarning ({ name, code, message, unlimited = false } = {}) {
   warning.message = message
   warning.unlimited = unlimited
   warning.code = code
+  warning[kWarningFn] = warningFn
+  warning[kWarningSpyData] = null
 
   /**
-   * Formats the warning message.
-   * @param {*} [a] Possible message interpolation value.
-   * @param {*} [b] Possible message interpolation value.
-   * @param {*} [c] Possible message interpolation value.
-   * @returns {string} The formatted warning message.
-   */
+ * Formats the warning message.
+ * @param {*} [a] Possible message interpolation value.
+ * @param {*} [b] Possible message interpolation value.
+ * @param {*} [c] Possible message interpolation value.
+ * @returns {string} The formatted warning message.
+ */
   warning.format = function (a, b, c) {
     let formatted
     if (a && b && c) {
@@ -116,9 +183,10 @@ function createWarning ({ name, code, message, unlimited = false } = {}) {
  * @namespace
  * @property {function} createWarning - Creates a warning item.
  * @property {function} createDeprecation - Creates a deprecation warning item.
+ * @property {function} spyWarning - Spy a warning item.
  * @property {ProcessWarning} processWarning - Represents the process warning functionality.
  */
-const out = { createWarning, createDeprecation }
+const out = { createWarning, createDeprecation, spyWarning }
 module.exports = out
 module.exports.default = out
 module.exports.processWarning = out
diff --git a/test/emit-once-only.test.js b/test/emit-once-only.test.js
index 4d5bc1f..cf9818c 100644
--- a/test/emit-once-only.test.js
+++ b/test/emit-once-only.test.js
@@ -5,7 +5,7 @@ const { createWarning } = require('..')
 const { withResolvers } = require('./promise')
 
 test('emit should emit a given code only once', t => {
-  t.plan(4)
+  t.plan(6)
 
   const { promise, resolve } = withResolvers()
 
@@ -22,8 +22,8 @@ test('emit should emit a given code only once', t => {
     code: 'CODE',
     message: 'Hello world'
   })
-  warn()
-  warn()
+  t.assert.strictEqual(warn(), true)
+  t.assert.strictEqual(warn(), false)
   setImmediate(() => {
     process.removeListener('warning', onWarning)
     resolve()
diff --git a/test/emit-reset.test.js b/test/emit-reset.test.js
index 1a31a4c..c5e6216 100644
--- a/test/emit-reset.test.js
+++ b/test/emit-reset.test.js
@@ -5,7 +5,7 @@ const { createWarning } = require('../')
 const { withResolvers } = require('./promise')
 
 test('a limited warning can be re-set', t => {
-  t.plan(4)
+  t.plan(7)
 
   const { promise, resolve } = withResolvers()
   let count = 0
@@ -20,14 +20,14 @@ test('a limited warning can be re-set', t => {
     message: 'Hello world'
   })
 
-  warn()
+  t.assert.strictEqual(warn(), true)
   t.assert.ok(warn.emitted)
 
-  warn()
+  t.assert.strictEqual(warn(), false)
   t.assert.ok(warn.emitted)
 
   warn.emitted = false
-  warn()
+  t.assert.strictEqual(warn(), true)
   t.assert.ok(warn.emitted)
 
   setImmediate(() => {
diff --git a/test/emit-unlimited.test.js b/test/emit-unlimited.test.js
index 3bf4780..2511e92 100644
--- a/test/emit-unlimited.test.js
+++ b/test/emit-unlimited.test.js
@@ -5,7 +5,7 @@ const { createWarning } = require('..')
 const { withResolvers } = require('./promise')
 
 test('emit should emit a given code unlimited times', t => {
-  t.plan(50)
+  t.plan(60)
 
   let runs = 0
   const expectedRun = []
@@ -31,7 +31,7 @@ test('emit should emit a given code unlimited times', t => {
 
   for (let i = 0; i < times; i++) {
     expectedRun.push(i)
-    warn()
+    t.assert.strictEqual(warn(), true)
   }
   setImmediate(() => {
     process.removeListener('warning', onWarning)
diff --git a/test/spy-warning.test.js b/test/spy-warning.test.js
new file mode 100644
index 0000000..9634a98
--- /dev/null
+++ b/test/spy-warning.test.js
@@ -0,0 +1,143 @@
+'use strict'
+
+const { test } = require('node:test')
+const { createWarning } = require('..')
+const { spyWarning } = require('..')
+
+test('Spy ProcessWarning - unlimited: false', t => {
+  const warning = createWarning({
+    name: 'Warning',
+    code: 'WRN',
+    message: 'Hello %s'
+  })
+  const spyData = spyWarning(warning)
+
+  t.assert.strictEqual(warning.emitted, false)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(), 0)
+
+  warning('World')
+  t.assert.strictEqual(warning.emitted, true)
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World'])
+  t.assert.strictEqual(spyData.calls[0].result, true)
+  t.assert.strictEqual(spyData.callCount(), 1)
+
+  warning('World')
+  t.assert.strictEqual(warning.emitted, true)
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World'])
+  t.assert.strictEqual(spyData.calls[0].result, true)
+  t.assert.deepStrictEqual(spyData.calls[1].arguments, ['World'])
+  t.assert.strictEqual(spyData.calls[1].result, false)
+  t.assert.strictEqual(spyData.callCount(), 2)
+
+  spyData.reset()
+  t.assert.strictEqual(warning.emitted, false)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(), 0)
+
+  warning('World')
+  t.assert.strictEqual(warning.emitted, true)
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World'])
+  t.assert.strictEqual(spyData.calls[0].result, true)
+  t.assert.strictEqual(spyData.callCount(), 1)
+
+  spyData.restore()
+  t.assert.strictEqual(warning.emitted, false)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(), 0)
+
+  warning('World')
+  t.assert.strictEqual(warning.emitted, true)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(), 0)
+})
+
+test('Spy ProcessWarning - unlimited: true', t => {
+  const warning = createWarning({
+    name: 'Warning',
+    code: 'WRN',
+    message: 'Hello %s',
+    unlimited: true
+  })
+  const spyData = spyWarning(warning)
+
+  t.assert.strictEqual(warning.emitted, false)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(), 0)
+
+  warning('World')
+  t.assert.strictEqual(warning.emitted, true)
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World'])
+  t.assert.strictEqual(spyData.calls[0].result, true)
+  t.assert.strictEqual(spyData.callCount(), 1)
+
+  warning('World')
+  t.assert.strictEqual(warning.emitted, true)
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World'])
+  t.assert.strictEqual(spyData.calls[0].result, true)
+  t.assert.deepStrictEqual(spyData.calls[1].arguments, ['World'])
+  t.assert.strictEqual(spyData.calls[1].result, true)
+  t.assert.strictEqual(spyData.callCount(), 2)
+
+  spyData.reset()
+  t.assert.strictEqual(warning.emitted, false)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(), 0)
+
+  warning('World')
+  t.assert.strictEqual(warning.emitted, true)
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World'])
+  t.assert.strictEqual(spyData.calls[0].result, true)
+  t.assert.strictEqual(spyData.callCount(), 1)
+
+  spyData.restore()
+  t.assert.strictEqual(warning.emitted, false)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(), 0)
+
+  warning('World')
+  t.assert.strictEqual(warning.emitted, true)
+  t.assert.deepStrictEqual(spyData.calls, [])
+  t.assert.strictEqual(spyData.callCount(), 0)
+})
+
+test('Spy ProcessWarning - calls[].arguments', t => {
+  const warning = createWarning({
+    name: 'Warning',
+    code: 'WRN',
+    message: 'Hello %s'
+  })
+  const spyData = spyWarning(warning)
+
+  warning(undefined)
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, [])
+  spyData.reset()
+
+  warning()
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, [])
+  spyData.reset()
+
+  warning('World')
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World'])
+  spyData.reset()
+
+  warning('World', 'Hello')
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World', 'Hello'])
+  spyData.reset()
+
+  warning(undefined, 'Hello')
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, [undefined, 'Hello'])
+  spyData.reset()
+
+  warning('World', 'Hello', 'World')
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World', 'Hello', 'World'])
+  spyData.reset()
+
+  warning('World', undefined, 'World')
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, ['World', undefined, 'World'])
+  spyData.reset()
+
+  warning(undefined, 'Hello', 'World')
+  t.assert.deepStrictEqual(spyData.calls[0].arguments, [undefined, 'Hello', 'World'])
+  spyData.reset()
+})
diff --git a/types/index.d.ts b/types/index.d.ts
index 0728405..2ecbb29 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1,6 +1,6 @@
 declare namespace processWarning {
   export interface WarningItem {
-    (a?: any, b?: any, c?: any): void;
+    (a?: any, b?: any, c?: any): boolean;
     name: string;
     code: string;
     message: string;
@@ -22,13 +22,27 @@ declare namespace processWarning {
     unlimited?: boolean;
   }
 
+  export type WarningSpyData = {
+    calls: WarningCallData[],
+    callCount(): number
+    reset(): void
+    restore(): void
+  }
+
+  export type WarningCallData = {
+    arguments: unknown[]
+    result: boolean
+  }
+
   export type ProcessWarning = {
     createWarning(params: WarningOptions): WarningItem;
     createDeprecation(params: DeprecationOptions): WarningItem;
+    spyWarning(warning: WarningItem): WarningSpyData
   }
 
   export function createWarning (params: WarningOptions): WarningItem
   export function createDeprecation (params: DeprecationOptions): WarningItem
+  export function spyWarning (warning: WarningItem): WarningSpyData
 
   const processWarning: ProcessWarning
   export { processWarning as default }
diff --git a/types/index.tst.ts b/types/index.tst.ts
index 2f953af..2de4687 100644
--- a/types/index.tst.ts
+++ b/types/index.tst.ts
@@ -1,5 +1,5 @@
 import { expect } from 'tstyche'
-import { createWarning, createDeprecation } from '..'
+import { createDeprecation, createWarning, spyWarning, WarningCallData, WarningSpyData } from '..'
 
 const WarnInstance = createWarning({
   name: 'TypeScriptWarning',
@@ -13,9 +13,9 @@ expect(WarnInstance.name).type.toBe<string>()
 expect(WarnInstance.emitted).type.toBe<boolean>()
 expect(WarnInstance.unlimited).type.toBe<boolean>()
 
-expect(WarnInstance()).type.toBe<void>()
-expect(WarnInstance('foo')).type.toBe<void>()
-expect(WarnInstance('foo', 'bar')).type.toBe<void>()
+expect(WarnInstance()).type.toBe<boolean>()
+expect(WarnInstance('foo')).type.toBe<boolean>()
+expect(WarnInstance('foo', 'bar')).type.toBe<boolean>()
 
 const buildWarnUnlimited = createWarning({
   name: 'TypeScriptWarning',
@@ -33,6 +33,16 @@ const DeprecationInstance = createDeprecation({
 
 expect(DeprecationInstance.code).type.toBe<string>()
 
-expect(DeprecationInstance()).type.toBe<void>()
-expect(DeprecationInstance('foo')).type.toBe<void>()
-expect(DeprecationInstance('foo', 'bar')).type.toBe<void>()
+expect(DeprecationInstance()).type.toBe<boolean>()
+expect(DeprecationInstance('foo')).type.toBe<boolean>()
+expect(DeprecationInstance('foo', 'bar')).type.toBe<boolean>()
+
+const spyData = spyWarning(WarnInstance)
+expect(spyData).type.toBe<WarningSpyData>()
+expect(spyData.calls).type.toBe<WarningCallData[]>()
+expect(spyData.callCount).type.toBe<(() => number)>()
+expect(spyData.callCount()).type.toBe<number>()
+expect(spyData.reset).type.toBe<(() => void)>()
+expect(spyData.reset()).type.toBe<void>()
+expect(spyData.restore).type.toBe<(() => void)>()
+expect(spyData.restore()).type.toBe<void>()