testing: add more cases for AverageTest (#6384)

* testing: add more cases for AverageTest

* checkstyle: fix formatting

Author: alxkm

src/test/java/com/thealgorithms/maths/AverageTest.java

@@ -1,33 +1,48 @@
 package com.thealgorithms.maths;
 
-import org.junit.jupiter.api.Assertions;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 public class AverageTest {
 
     private static final double SMALL_VALUE = 0.00001d;
 
-    @Test
-    public void testAverageDouble12() {
-        double[] numbers = {3d, 6d, 9d, 12d, 15d, 18d, 21d};
-        Assertions.assertEquals(12d, Average.average(numbers), SMALL_VALUE);
+    @ParameterizedTest(name = "average({0}) should be approximately {1}")
+    @MethodSource("provideDoubleArrays")
+    void testAverageDouble(double[] numbers, double expected) {
+        assertEquals(expected, Average.average(numbers), SMALL_VALUE);
     }
 
-    @Test
-    public void testAverageDouble20() {
-        double[] numbers = {5d, 10d, 15d, 20d, 25d, 30d, 35d};
-        Assertions.assertEquals(20d, Average.average(numbers), SMALL_VALUE);
+    @ParameterizedTest(name = "average({0}) should be {1}")
+    @MethodSource("provideIntArrays")
+    void testAverageInt(int[] numbers, long expected) {
+        assertEquals(expected, Average.average(numbers));
     }
 
     @Test
-    public void testAverageDouble() {
-        double[] numbers = {1d, 2d, 3d, 4d, 5d, 6d, 7d, 8d};
-        Assertions.assertEquals(4.5d, Average.average(numbers), SMALL_VALUE);
+    void testAverageDoubleThrowsExceptionOnNullOrEmpty() {
+        assertThrows(IllegalArgumentException.class, () -> Average.average((double[]) null));
+        assertThrows(IllegalArgumentException.class, () -> Average.average(new double[0]));
     }
 
     @Test
-    public void testAverageInt() {
-        int[] numbers = {2, 4, 10};
-        Assertions.assertEquals(5, Average.average(numbers));
+    void testAverageIntThrowsExceptionOnNullOrEmpty() {
+        assertThrows(IllegalArgumentException.class, () -> Average.average((int[]) null));
+        assertThrows(IllegalArgumentException.class, () -> Average.average(new int[0]));
+    }
+
+    private static Stream<Arguments> provideDoubleArrays() {
+        return Stream.of(Arguments.of(new double[] {3d, 6d, 9d, 12d, 15d, 18d, 21d}, 12d), Arguments.of(new double[] {5d, 10d, 15d, 20d, 25d, 30d, 35d}, 20d), Arguments.of(new double[] {1d, 2d, 3d, 4d, 5d, 6d, 7d, 8d}, 4.5d), Arguments.of(new double[] {0d, 0d, 0d}, 0d),
+            Arguments.of(new double[] {-1d, -2d, -3d}, -2d), Arguments.of(new double[] {1e-10, 1e-10, 1e-10}, 1e-10));
+    }
+
+    private static Stream<Arguments> provideIntArrays() {
+        return Stream.of(Arguments.of(new int[] {2, 4, 10}, 5L), Arguments.of(new int[] {0, 0, 0}, 0L), Arguments.of(new int[] {-1, -2, -3}, -2L), Arguments.of(new int[] {1, 1, 1, 1, 1}, 1L));
     }
 }