Create ShellSortTest (TheAlgorithms#3783)

Co-authored-by: Debasish Biswas <debasishbsws.abc@gmail.com>

Author: hyeonmin2

src/test/java/com/thealgorithms/sorts/ShellSortTest.java

@@ -0,0 +1,67 @@
+package com.thealgorithms.sorts;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class ShellSortTest {
+    
+    private ShellSort shellSort = new ShellSort();
+    
+    @Test
+    public void ShellSortEmptyArray() {
+        Integer[] inputArray = {};
+        Integer[] outputArray = shellSort.sort(inputArray);
+        Integer[] expectedOutput = {};
+        assertArrayEquals(outputArray, expectedOutput);
+    }
+
+    @Test
+    public void ShellSortSingleIntegerArray() {
+        Integer[] inputArray = { 4 };
+        Integer[] outputArray = shellSort.sort(inputArray);
+        Integer[] expectedOutput = { 4 };
+        assertArrayEquals(outputArray, expectedOutput);
+    }
+
+    @Test
+    public void ShellSortSingleStringArray() {
+        String[] inputArray = { "s" };
+        String[] outputArray = shellSort.sort(inputArray);
+        String[] expectedOutput = { "s" };
+        assertArrayEquals(outputArray, expectedOutput);
+    }
+
+    @Test
+    public void ShellSortNonDuplicateIntegerArray() {
+        Integer[] inputArray = { 6, -1, 99, 27, -15, 23, -36 };
+        Integer[] outputArray = shellSort.sort(inputArray);
+        Integer[] expectedOutput = { -36, -15, -1, 6, 23, 27, 99};
+        assertArrayEquals(outputArray, expectedOutput);
+    }
+    
+    @Test
+    public void ShellSortDuplicateIntegerArray() {
+        Integer[] inputArray = { 6, -1, 27, -15, 23, 27, -36, 23 };
+        Integer[] outputArray = shellSort.sort(inputArray);
+        Integer[] expectedOutput = { -36, -15, -1, 6, 23, 23, 27, 27};
+        assertArrayEquals(outputArray, expectedOutput);
+    }
+
+    @Test
+    public void ShellSortNonDuplicateStringArray() {
+        String[] inputArray = { "s", "b", "k", "a", "d", "c", "h" };
+        String[] outputArray = shellSort.sort(inputArray);
+        String[] expectedOutput = {"a", "b", "c", "d", "h", "k", "s" };
+        assertArrayEquals(outputArray, expectedOutput);
+    }
+
+    @Test
+    public void ShellSortDuplicateStringArray() {
+        String[] inputArray = { "s", "b", "d", "a", "d", "c", "h", "b" };
+        String[] outputArray = shellSort.sort(inputArray);
+        String[] expectedOutput = {"a", "b", "b", "c", "d", "d", "h", "s" };
+        assertArrayEquals(outputArray, expectedOutput);
+    }
+
+}