Create RelativityTest.java

Test file created for Relativity.java.

Author: kvadrik

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

@@ -0,0 +1,74 @@
+package com.thealgorithms.physics;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the Relativity utility class.
+ */
+final class RelativityTest {
+
+    // A small tolerance (delta) for comparing floating-point numbers
+    private static final double DELTA = 1e-9;
+    private static final double C = Relativity.SPEED_OF_LIGHT;
+	
+	@Test
+	@DisplayName("Test the gamma parameter")
+	void testGamma() {
+		double myGamma = Relativity.gamma(0.6*C);
+		assertEquals(1.25, myGamma, DELTA);
+	}
+	
+	@Test
+	@DisplayName("Test the length contraction")
+	void testLengthContraction() {
+		double myLength = Relativity.lengthContraction(5.0, 0.8*C);
+		assertEquals(3.0, myLength, DELTA);
+	}
+	
+	@Test
+	@DisplayName("Test the time dilation")
+	void testTimeDilation() {
+		double myTime = Relativity.timeDilation(4.0, 0.6*C);
+		assertEquals(5.0, myTime, DELTA);
+	}
+	
+	@Test
+	@DisplayName("Test the velocity addition in the same direction")
+	void testVelocityAddition() {
+		double myVelocity = Relativity.velocityAddition(0.8*C, 0.75*C);
+		assertEquals(0.125*C, myVelocity, DELTA);
+	}
+	
+	@Test
+	@DisplayName("Test the velocity addition in different directions")
+	void testVelocityAddition() {
+		double myVelocity = Relativity.velocityAddition(0.8*C, -0.75*C);
+		assertEquals(0.96875*C, myVelocity, DELTA);
+	}
+
+	@Test
+	@DisplayName("Test the velocity addition with the speed of light")
+	void testVelocityAddition() {
+		double myVelocity = Relativity.velocityAddition(C, 0.7*C);
+		assertEquals(C, myVelocity, DELTA);
+	}	
+	
+	@Test
+    @DisplayName("Test invalid inputs throw exception")
+    void testInvalidOrbitalVelocityInputs() {
+        assertThrows(IllegalArgumentException.class, () -> Relativity.gamma(1.2*C));
+		assertThrows(IllegalArgumentException.class, () -> Relativity.gamma(-C));
+        assertThrows(IllegalArgumentException.class, () -> Relativity.lengthContraction(-1.0, 0.6*C));
+		assertThrows(IllegalArgumentException.class, () -> Relativity.lengthContraction(1.0, 1.5*C));
+        assertThrows(IllegalArgumentException.class, () -> Relativity.timeDilation(-5.0, -0.8*C));
+		assertThrows(IllegalArgumentException.class, () -> Relativity.timeDilation(5.0, C));
+        assertThrows(IllegalArgumentException.class, () -> Relativity.velocityAddition(0.3*C, -C));
+		assertThrows(IllegalArgumentException.class, () -> Relativity.velocityAddition(1.4*C, 0.2*C));
+		assertThrows(IllegalArgumentException.class, () -> Relativity.velocityAddition(-0.4*C, 1.2*C));
+    }
+}