Refactor SnellLawTest for clarity and accuracy

Author: Dsannue

src/test/java/com/thealgorithms/physics/SnellLawTest.java

@@ -4,29 +4,40 @@
 import org.junit.jupiter.api.Test;
 
 public class SnellLawTest {
-//tests for example environmet
+
     @Test
-    public void testCalculateRefractionAngle() {
+    public void testRefractedAngle() {
         double n1 = 1.0;  // air
         double n2 = 1.5;  // glass
-        double theta1 = Math.toRadians(30); // 30 grados
-        
-        double theta2 = SnellsLaw.calculateRefractionAngle(n1, n2, theta1);
-        
-        // expected value using: sin(theta2) = n1/n2 * sin(theta1)
+        double theta1 = Math.toRadians(30);
+
+        double theta2 = SnellLaw.refractedAngle(n1, n2, theta1);
+
         double expected = Math.asin((n1 / n2) * Math.sin(theta1));
 
-        assertEquals(expected, theta2, 1e-9);
+        assertEquals(expected, theta2, 1e-12);
     }
-//tests for total refraction
+
     @Test
-    public void testInvalidRefractiveIndex() {
+    public void testTotalInternalReflection() {
+        // total internal reflection happens when n1 > n2 AND theta1 is large
+        double n1 = 1.5;
+        double n2 = 1.0;
+        double theta1 = Math.toRadians(60); // large enough angle
+
         assertThrows(IllegalArgumentException.class, () -> {
-            SnellsLaw.calculateRefractionAngle(-1, 1.5, 0.5);
+            SnellLaw.refractedAngle(n1, n2, theta1);
         });
+    }
 
-        assertThrows(IllegalArgumentException.class, () -> {
-            SnellsLaw.calculateRefractionAngle(1, 0, 0.5);
+    @Test
+    public void testNoTotalInternalReflectionAtLowAngles() {
+        double n1 = 1.5;
+        double n2 = 1.0;
+        double theta1 = Math.toRadians(10);
+
+        assertDoesNotThrow(() -> {
+            SnellLaw.refractedAngle(n1, n2, theta1);
         });
     }
 }