diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 3c6bddc..3a9b40c 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -21,7 +21,7 @@ repositories {
 dependencies {
     // Use JUnit Jupiter for testing.
     testImplementation(libs.junit.jupiter)
-    testImplementation("org.assertj:assertj-core:3.25.3")
+    testImplementation(libs.assertj.core)
 
     testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 
diff --git a/app/build.gradle.sonar.kts b/app/build.gradle.sonar.kts
index a4c9d9d..77f650c 100644
--- a/app/build.gradle.sonar.kts
+++ b/app/build.gradle.sonar.kts
@@ -22,7 +22,7 @@ repositories {
 dependencies {
     // Use JUnit Jupiter for testing.
     testImplementation(libs.junit.jupiter)
-    testImplementation("org.assertj:assertj-core:3.25.3")
+    testImplementation(libs.assertj.core)
 
     testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index a4c9d1c..4d3bc9b 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -4,7 +4,9 @@
 [versions]
 # guava = "32.1.3-jre"
 junit-jupiter = "5.10.0"
+assertj       = "3.25.3"
 
 [libraries]
 # guava = { module = "com.google.guava:guava", version.ref = "guava" }
 junit-jupiter = { module = "org.junit.jupiter:junit-jupiter", version.ref = "junit-jupiter" }
+assertj-core  = { module = "org.assertj:assertj-core", version.ref = "assertj" }