Add gatherer for fixedwindow

Author: ZahidFKhan

src/test/java/com/github/streams/practice/gatherers/ScanTest.java

@@ -0,0 +1,29 @@
+package com.github.streams.practice.gatherers;
+
+import java.util.List;
+import java.util.stream.Gatherers;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledOnJre;
+import org.junit.jupiter.api.condition.JRE;
+
+/// The windowFixed gatherer is an intermediate stream operation used to partition an input stream
+// into a stream of non-overlapping, fixed-size lists (or "windows"). This is also commonly known as
+// chunking or batching a stream.
+///
+/// The gatherer ensures that every element is consumed by exactly one window.
+///
+///
+class WindowFixedTest {
+  @Test
+  @EnabledOnJre(JRE.JAVA_25)
+  void windowFixedTest() {
+    final List<Integer> input = List.of(1, 2, 3, 4, 5, 6, 7, 8);
+    final int windowSize = 2;
+
+    final var output = input.stream().gather(Gatherers.windowFixed(windowSize)).toList();
+    final var expected = List.of(List.of(1, 2), List.of(3, 4), List.of(5, 6), List.of(7, 8));
+
+    Assertions.assertEquals(expected, output);
+  }
+}