diff --git a/README.md b/README.md
index 00343d3..768bb3d 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,14 @@ A simple REST application with Kotlin
 ./gradlew clean build
 ```
 
+## Testing Application
+
+```console
+./gradlew clean test
+```
+
+Minimum coverage is 80%, and report in _build/jacocoHtml/index.html_
+
 ## Running Application
 
 ```console
diff --git a/build.gradle b/build.gradle
index fe95e65..aaa90dc 100644
--- a/build.gradle
+++ b/build.gradle
@@ -6,7 +6,7 @@ plugins {
 
 mainClassName = 'br.com.dev.shoppingcart.AppKt'
 group = 'br.com.dev'
-version = '2.1.2'
+version = '2.1.3'
 
 repositories {
     mavenCentral()
diff --git a/src/main/kotlin/br/com/dev/shoppingcart/domain/repository/ProductRepository.kt b/src/main/kotlin/br/com/dev/shoppingcart/domain/repository/ProductRepository.kt
index c956f16..4671dfb 100644
--- a/src/main/kotlin/br/com/dev/shoppingcart/domain/repository/ProductRepository.kt
+++ b/src/main/kotlin/br/com/dev/shoppingcart/domain/repository/ProductRepository.kt
@@ -5,7 +5,7 @@ import br.com.dev.shoppingcart.web.dto.ProductDTO
 
 class ProductRepository(private val products: MutableList<Product>) {
 
-    fun findProductById(productId: Long) = products.firstOrNull {
+    fun findProductById(productId: Long): Product? = products.firstOrNull {
         it.id == productId
     }
 
diff --git a/src/test/kotlin/br/com/dev/shoppingcart/domain/repository/CartRepositoryTest.kt b/src/test/kotlin/br/com/dev/shoppingcart/domain/repository/CartRepositoryTest.kt
index 8c118f6..a4b2ef1 100644
--- a/src/test/kotlin/br/com/dev/shoppingcart/domain/repository/CartRepositoryTest.kt
+++ b/src/test/kotlin/br/com/dev/shoppingcart/domain/repository/CartRepositoryTest.kt
@@ -6,7 +6,6 @@ import br.com.dev.shoppingcart.domain.model.Product
 import io.mockk.impl.annotations.MockK
 import io.mockk.junit5.MockKExtension
 import org.assertj.core.api.Assertions.assertThat
-import org.junit.jupiter.api.BeforeEach
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.extension.ExtendWith
 
@@ -15,20 +14,12 @@ internal class CartRepositoryTest {
 
     private lateinit var cut: CartRepository
 
-    @MockK
-    private lateinit var carts: MutableList<Cart>
-
     @MockK
     private lateinit var cartProducts: MutableList<CartProduct>
 
     @MockK
     private lateinit var products: MutableList<Product>
 
-    @BeforeEach
-    fun setUp() {
-        this.cut = CartRepository(carts, cartProducts, products)
-    }
-
     @Test
     fun `given an user id if it exists must return a list of carts`() {
         // arrange
diff --git a/src/test/kotlin/br/com/dev/shoppingcart/domain/repository/ProductRepositoryTest.kt b/src/test/kotlin/br/com/dev/shoppingcart/domain/repository/ProductRepositoryTest.kt
new file mode 100644
index 0000000..f517a97
--- /dev/null
+++ b/src/test/kotlin/br/com/dev/shoppingcart/domain/repository/ProductRepositoryTest.kt
@@ -0,0 +1,70 @@
+package br.com.dev.shoppingcart.domain.repository
+
+import br.com.dev.shoppingcart.domain.model.Product
+import br.com.dev.shoppingcart.mocks.ProductMock
+import br.com.dev.shoppingcart.web.dto.ProductDTO
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+
+internal class ProductRepositoryTest {
+
+    private lateinit var cut: ProductRepository
+
+    @Test
+    fun `given a product id when a product with that id exists must return it`() {
+        // arrange
+        this.cut = ProductRepository(ProductMock.getListWithThreeProducts())
+
+        // act
+        val product = this.cut.findProductById(1)
+
+        // assert
+        assertThat(product).isNotNull
+        assertThat(product?.id).isEqualTo(1)
+    }
+
+    @Test
+    fun `given a product id when a product with that id does not exists must return null`() {
+        // arrange
+        this.cut = ProductRepository(ProductMock.getListWithThreeProducts())
+
+        // act
+        val product = this.cut.findProductById(100)
+
+        // assert
+        assertThat(product).isNull()
+    }
+
+    @Test
+    fun `given an empty list of products when adding a new one must be of size one and id 1`() {
+        // arrange
+        val products = mutableListOf<Product>()
+        this.cut = ProductRepository(products)
+
+        // act
+        val product =
+            this.cut.saveProduct(ProductDTO(name = "Test", price = 100.0, description = "", category = "test"))
+
+        // assert
+        assertThat(product).isNotNull
+        assertThat(product.id).isEqualTo(1)
+
+        assertThat(products).size().isEqualTo(1)
+    }
+
+    @Test
+    fun `given a list of products with one element when adding a new one must be of size two`() {
+        // arrange
+        val products = ProductMock.getListWithOneProduct()
+        
+        this.cut = ProductRepository(products)
+
+        // act
+        val product =
+            this.cut.saveProduct(ProductDTO(name = "Test", price = 100.0, description = "", category = "test"))
+
+        // assert
+        assertThat(product).isNotNull
+        assertThat(products).size().isEqualTo(2)
+    }
+}
\ No newline at end of file
diff --git a/src/test/kotlin/br/com/dev/shoppingcart/mocks/ProductMock.kt b/src/test/kotlin/br/com/dev/shoppingcart/mocks/ProductMock.kt
index 9947eb5..05289a1 100644
--- a/src/test/kotlin/br/com/dev/shoppingcart/mocks/ProductMock.kt
+++ b/src/test/kotlin/br/com/dev/shoppingcart/mocks/ProductMock.kt
@@ -8,9 +8,9 @@ object ProductMock {
     fun getOneProductWithShorts() = Product(2, "Shorts", 20.00, "", "Vestuário")
     fun getOneProductWithTenis() = Product(3, "Tênis", 159.00, "", "Vestuário")
 
-    fun getListWithOneProduct() = listOf(Product(1, "Camiseta", 100.00, "", "Vestuário"))
+    fun getListWithOneProduct() = mutableListOf(Product(1, "Camiseta", 100.00, "", "Vestuário"))
 
-    fun getListWithThreeProducts() = listOf(
+    fun getListWithThreeProducts() = mutableListOf(
         getOneProductWithCamiseta(),
         getOneProductWithShorts(),
         getOneProductWithTenis()