Some comments in code

src/test/java/eu/ztsh/training/hackerrank/EnvironmentTest.java

@@ -2,6 +2,7 @@ package eu.ztsh.training.hackerrank;
 
 import java.util.List;
 import java.util.Scanner;
+
 import eu.ztsh.training.hackerrank.SolutionClassDescription.FieldModifier;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.DisplayName;

src/test/java/eu/ztsh/training/hackerrank/HackerRankTest.java

@@ -7,13 +7,18 @@ import java.io.PrintStream;
 import java.lang.reflect.InvocationTargetException;
 import java.util.Arrays;
 import java.util.List;
+
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 
+/**
+ * Common class with all the necessary logic
+ */
 public abstract class HackerRankTest {
 
     @BeforeAll
     public static void setUpStreams() {
+        // Redirect stdout & stderr to own streams
         System.setOut(new PrintStream(outContent));
         System.setErr(new PrintStream(errContent));
     }
@@ -27,14 +32,19 @@ public abstract class HackerRankTest {
 
     protected List<String> invoke(List<String> input) {
         try {
+            // reset our stdout as check is based on it
             outContent.reset();
+            // write content to args of Solution#main
             writeLines(input);
+            // check if scanner has other name than "scanner"
             if (getSolutionClassDescription().fieldName() != null) {
                 ReflectionHelper.reloadScanner(getSolutionClassDescription());
             }
+            // run Solution#main
             getSolutionClassDescription().targetClass()
                     .getMethod("main", String[].class)
                     .invoke(null, (Object) new String[]{});
+            // return intercepted output
             return readLines();
         } catch (final NoSuchMethodException | InvocationTargetException | IllegalAccessException |
                        NoSuchFieldException e) {

src/test/java/eu/ztsh/training/hackerrank/ReflectionHelper.java

@@ -5,9 +5,12 @@ import java.lang.invoke.VarHandle;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.Scanner;
+
 import eu.ztsh.training.hackerrank.SolutionClassDescription.FieldModifier;
 
-
+/**
+ * Util that helps with scanner declared outside Solution#main
+ */
 public class ReflectionHelper {
 
     // https://stackoverflow.com/a/56043252
@@ -21,7 +24,15 @@ public class ReflectionHelper {
         }
     }
 
-    static void reloadScanner(SolutionClassDescription description) throws NoSuchFieldException, IllegalAccessException {
+    /**
+     * Modify scanner field to substitute it with custom readable one
+     *
+     * @param description Solution class parameters
+     * @throws NoSuchFieldException   when there description.fieldName points to incorrect name
+     * @throws IllegalAccessException on scanner substitution error
+     */
+    static void reloadScanner(SolutionClassDescription description)
+            throws NoSuchFieldException, IllegalAccessException {
         // https://stackoverflow.com/a/3301720
         var scannerField = description.hasModifier(FieldModifier.STATIC)
                 ? description.targetClass().getDeclaredField(description.fieldName())

src/test/java/eu/ztsh/training/hackerrank/SolutionClassDescription.java

@@ -2,6 +2,13 @@ package eu.ztsh.training.hackerrank;
 
 import java.util.Arrays;
 
+/**
+ * Solution params definition
+ *
+ * @param targetClass Solution
+ * @param fieldName   scanner field name
+ * @param modifiers   scanner field modifiers
+ */
 public record SolutionClassDescription(Class<?> targetClass, String fieldName, FieldModifier[] modifiers) {
 
     SolutionClassDescription(Class<?> targetClass) {