diff --git a/pom.xml b/pom.xml
index e79f1d9d..5856c0a3 100644
--- a/pom.xml
+++ b/pom.xml
@@ -145,6 +145,12 @@ SOFTWARE.
test
+
+ org.junit.jupiter
+ junit-jupiter-engine
+
+ test
+
org.junit.jupiter
junit-jupiter-params
@@ -158,8 +164,8 @@ SOFTWARE.
test
- org.junit.jupiter
- junit-jupiter-engine
+ com.jcabi
+ jcabi-matchers
test
diff --git a/src/main/java/org/eolang/opeo/Instruction.java b/src/main/java/org/eolang/opeo/Instruction.java
index 4c5e7315..67363f6c 100644
--- a/src/main/java/org/eolang/opeo/Instruction.java
+++ b/src/main/java/org/eolang/opeo/Instruction.java
@@ -23,6 +23,7 @@
*/
package org.eolang.opeo;
+import java.util.Collections;
import java.util.List;
import lombok.ToString;
@@ -43,7 +44,7 @@ public final class Instruction {
/**
* Operands.
*/
- private final List