refactor: Enhance docs, code, add tests in HeronsFormula (#6746)

* refactor: Enhance docs, code, add tests in `HeronsFormula`

* Fix lint

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

@@ -3,37 +3,141 @@ package com.thealgorithms.maths;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
-public class HeronsFormulaTest {
+/**
+ * Test cases for {@link HeronsFormula}.
+ */
+class HeronsFormulaTest {
+
+    private static final double EPSILON = 1e-10;
 
     @Test
-    void test1() {
-        Assertions.assertEquals(HeronsFormula.herons(3, 4, 5), 6.0);
+    void testRightTriangleThreeFourFive() {
+        Assertions.assertEquals(6.0, HeronsFormula.herons(3, 4, 5), EPSILON);
     }
 
     @Test
-    void test2() {
-        Assertions.assertEquals(HeronsFormula.herons(24, 30, 18), 216.0);
+    void testTriangleTwentyFourThirtyEighteen() {
+        Assertions.assertEquals(216.0, HeronsFormula.herons(24, 30, 18), EPSILON);
     }
 
     @Test
-    void test3() {
-        Assertions.assertEquals(HeronsFormula.herons(1, 1, 1), 0.4330127018922193);
+    void testEquilateralTriangle() {
+        Assertions.assertEquals(0.4330127018922193, HeronsFormula.herons(1, 1, 1), EPSILON);
     }
 
     @Test
-    void test4() {
-        Assertions.assertEquals(HeronsFormula.herons(4, 5, 8), 8.181534085976786);
+    void testScaleneTriangleFourFiveEight() {
+        Assertions.assertEquals(8.181534085976786, HeronsFormula.herons(4, 5, 8), EPSILON);
     }
 
     @Test
-    public void testCalculateAreaWithInvalidInput() {
+    void testEquilateralTriangleLargeSides() {
+        final double side = 10.0;
+        final double expectedArea = Math.sqrt(3) / 4 * side * side;
+        Assertions.assertEquals(expectedArea, HeronsFormula.herons(side, side, side), EPSILON);
+    }
+
+    @Test
+    void testIsoscelesTriangle() {
+        Assertions.assertEquals(12.0, HeronsFormula.herons(5, 5, 6), EPSILON);
+    }
+
+    @Test
+    void testSmallTriangle() {
+        Assertions.assertEquals(0.4330127018922193, HeronsFormula.herons(1.0, 1.0, 1.0), EPSILON);
+    }
+
+    @Test
+    void testLargeTriangle() {
+        Assertions.assertEquals(600.0, HeronsFormula.herons(30, 40, 50), EPSILON);
+    }
+
+    @Test
+    void testDecimalSides() {
+        final double area = HeronsFormula.herons(2.5, 3.5, 4.0);
+        Assertions.assertTrue(area > 0);
+        Assertions.assertEquals(4.330127018922194, area, EPSILON);
+    }
+
+    @Test
+    void testDegenerateTriangleEqualToSumOfOtherTwo() {
         Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(1, 2, 3); });
-        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(2, 1, 3); });
-        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(3, 2, 1); });
-        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(1, 3, 2); });
+    }
 
-        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(1, 1, 0); });
-        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(1, 0, 1); });
+    @Test
+    void testDegenerateTriangleVariant2() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(2, 1, 3); });
+    }
+
+    @Test
+    void testDegenerateTriangleVariant3() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(3, 2, 1); });
+    }
+
+    @Test
+    void testDegenerateTriangleVariant4() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(1, 3, 2); });
+    }
+
+    @Test
+    void testInvalidTriangleSideGreaterThanSum() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(1, 1, 5); });
+    }
+
+    @Test
+    void testZeroFirstSide() {
         Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(0, 1, 1); });
     }
+
+    @Test
+    void testZeroSecondSide() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(1, 0, 1); });
+    }
+
+    @Test
+    void testZeroThirdSide() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(1, 1, 0); });
+    }
+
+    @Test
+    void testNegativeFirstSide() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(-1, 2, 2); });
+    }
+
+    @Test
+    void testNegativeSecondSide() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(2, -1, 2); });
+    }
+
+    @Test
+    void testNegativeThirdSide() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(2, 2, -1); });
+    }
+
+    @Test
+    void testAllNegativeSides() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(-1, -2, -3); });
+    }
+
+    @Test
+    void testAllZeroSides() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> { HeronsFormula.herons(0, 0, 0); });
+    }
+
+    @Test
+    void testVerySmallTriangle() {
+        final double result = HeronsFormula.herons(0.001, 0.001, 0.001);
+        Assertions.assertTrue(result > 0);
+        Assertions.assertTrue(result < 0.001);
+    }
+
+    @Test
+    void testRightTriangleFiveTwelveThirteen() {
+        Assertions.assertEquals(30.0, HeronsFormula.herons(5, 12, 13), EPSILON);
+    }
+
+    @Test
+    void testRightTriangleEightFifteenSeventeen() {
+        Assertions.assertEquals(60.0, HeronsFormula.herons(8, 15, 17), EPSILON);
+    }
 }