diff --git a/Jenkinsfile b/Jenkinsfile
index 131b0604e..0c161fe52 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -9,6 +9,9 @@ node {
     stage('Cleanup') {
       sh "./gradlew clean"
     }
+    stage('Test') {
+      sh "./gradlew test"
+    }
     stage('Build') {
       sh "./gradlew build"
     }
@@ -19,7 +22,7 @@ node {
   stage('Publish artifacts') {
     sh "./gradlew publish"
   }
-  stage('SonarQube') {
+  stage('SonarQube analysis') {
     withCredentials([string(credentialsId: 'SONAR_TOKEN', variable: 'SONAR_TOKEN')]) {
       sh "./gradlew sonarqube -Dsonar.login=$SONAR_TOKEN"
     }
diff --git a/build.gradle b/build.gradle
index 66896e406..407fcf357 100755
--- a/build.gradle
+++ b/build.gradle
@@ -11,6 +11,7 @@ buildscript {
 
 plugins {
     id "org.sonarqube" version "3.0"
+    id 'info.solidsoft.pitest' version '1.5.1'
 }
 
 repositories {
@@ -33,6 +34,11 @@ sonarqube {
 apply plugin: 'net.minecraftforge.gradle'
 apply plugin: 'eclipse'
 apply plugin: 'maven-publish'
+apply plugin: 'info.solidsoft.pitest'
+
+pitest {
+    junit5PluginVersion = "0.12"
+}
 
 version = '1.9.8'
 def env = System.getenv()
@@ -118,6 +124,10 @@ dependencies {
     compileOnly 'mouse-tweaks:MouseTweaks:2.13:mc1.16.2'
 
     runtimeOnly fg.deobf('crafting-tweaks:CraftingTweaks_1.16.2:12.1.0')
+
+    testImplementation('org.junit.jupiter:junit-jupiter-api:5.6.2')
+    testRuntime('org.junit.jupiter:junit-jupiter-engine:5.6.2')
+    testCompile group: 'org.assertj', name: 'assertj-core', version: '3.16.1'
 }
 
 jar {
@@ -160,6 +170,10 @@ artifacts {
     archives apiJar
 }
 
+test {
+    useJUnitPlatform()
+}
+
 publishing {
     publications {
         mavenJava(MavenPublication) {
diff --git a/src/main/java/com/refinedmods/refinedstorage/api/util/IStackList.java b/src/main/java/com/refinedmods/refinedstorage/api/util/IStackList.java
index 92969c2f3..4ed5bb2af 100644
--- a/src/main/java/com/refinedmods/refinedstorage/api/util/IStackList.java
+++ b/src/main/java/com/refinedmods/refinedstorage/api/util/IStackList.java
@@ -123,4 +123,9 @@ public interface IStackList<T> {
      */
     @Nonnull
     IStackList<T> copy();
+
+    /**
+     * @return the amount of elements in this list
+     */
+    int size();
 }
diff --git a/src/main/java/com/refinedmods/refinedstorage/apiimpl/util/FluidStackList.java b/src/main/java/com/refinedmods/refinedstorage/apiimpl/util/FluidStackList.java
index b08d518ee..3157fbe58 100644
--- a/src/main/java/com/refinedmods/refinedstorage/apiimpl/util/FluidStackList.java
+++ b/src/main/java/com/refinedmods/refinedstorage/apiimpl/util/FluidStackList.java
@@ -157,4 +157,9 @@ public class FluidStackList implements IStackList<FluidStack> {
 
         return list;
     }
+
+    @Override
+    public int size() {
+        return stacks.size();
+    }
 }
diff --git a/src/main/java/com/refinedmods/refinedstorage/apiimpl/util/ItemStackList.java b/src/main/java/com/refinedmods/refinedstorage/apiimpl/util/ItemStackList.java
index 48b221c75..385fabdb3 100644
--- a/src/main/java/com/refinedmods/refinedstorage/apiimpl/util/ItemStackList.java
+++ b/src/main/java/com/refinedmods/refinedstorage/apiimpl/util/ItemStackList.java
@@ -155,4 +155,9 @@ public class ItemStackList implements IStackList<ItemStack> {
 
         return list;
     }
+
+    @Override
+    public int size() {
+        return stacks.size();
+    }
 }