Add SlackTimeScheduling algorithm (#5814)

src/test/java/com/thealgorithms/scheduling/SlackTimeSchedulingTest.java

@@ -0,0 +1,48 @@
+package com.thealgorithms.scheduling;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class SlackTimeSchedulingTest {
+
+    private SlackTimeScheduling scheduler;
+
+    @BeforeEach
+    public void setup() {
+        scheduler = new SlackTimeScheduling();
+    }
+
+    @Test
+    public void testAddAndScheduleSingleTask() {
+        scheduler.addTask("Task1", 2, 5);
+        List<String> expected = List.of("Task1");
+        assertEquals(expected, scheduler.scheduleTasks());
+    }
+
+    @Test
+    public void testScheduleMultipleTasks() {
+        scheduler.addTask("Task1", 2, 5);
+        scheduler.addTask("Task2", 1, 4);
+        scheduler.addTask("Task3", 3, 7);
+        List<String> expected = List.of("Task1", "Task2", "Task3");
+        assertEquals(expected, scheduler.scheduleTasks());
+    }
+
+    @Test
+    public void testScheduleTasksWithSameSlackTime() {
+        scheduler.addTask("Task1", 2, 5);
+        scheduler.addTask("Task2", 3, 6);
+        scheduler.addTask("Task3", 1, 4);
+        List<String> expected = List.of("Task1", "Task2", "Task3");
+        assertEquals(expected, scheduler.scheduleTasks());
+    }
+
+    @Test
+    public void testEmptyScheduler() {
+        List<String> expected = List.of();
+        assertEquals(expected, scheduler.scheduleTasks());
+    }
+}