Add tests for AffineConverter.java (#5602)

Author: Hardvan

DIRECTORY.md

@@ -651,6 +651,7 @@
             * [VigenereTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/VigenereTest.java)
             * [XORCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/XORCipherTest.java)
           * conversions
+            * [AffineConverterTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/conversions/AffineConverterTest.java)
             * [AnyBaseToDecimalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/conversions/AnyBaseToDecimalTest.java)
             * [BinaryToDecimalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/conversions/BinaryToDecimalTest.java)
             * [BinaryToHexadecimalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/conversions/BinaryToHexadecimalTest.java)

src/test/java/com/thealgorithms/conversions/AffineConverterTest.java

@@ -0,0 +1,55 @@
+package com.thealgorithms.conversions;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class AffineConverterTest {
+
+    private AffineConverter converter;
+
+    @BeforeEach
+    void setUp() {
+        converter = new AffineConverter(2.0, 3.0);
+    }
+
+    @Test
+    void testConstructor() {
+        assertEquals(3.0, converter.convert(0.0), "Expected value when input is 0.0");
+        assertEquals(5.0, converter.convert(1.0), "Expected value when input is 1.0");
+        assertEquals(7.0, converter.convert(2.0), "Expected value when input is 2.0");
+    }
+
+    @Test
+    void testConvert() {
+        assertEquals(3.0, converter.convert(0.0), "Conversion at 0.0 should equal the intercept");
+        assertEquals(7.0, converter.convert(2.0), "2.0 should convert to 7.0");
+        assertEquals(11.0, converter.convert(4.0), "4.0 should convert to 11.0");
+    }
+
+    @Test
+    void testInvert() {
+        AffineConverter inverted = converter.invert();
+        assertEquals(0.0, inverted.convert(3.0), "Inverted converter should return 0.0 for input 3.0");
+        assertEquals(1.0, inverted.convert(5.0), "Inverted converter should return 1.0 for input 5.0");
+        assertEquals(2.0, inverted.convert(7.0), "Inverted converter should return 2.0 for input 7.0");
+    }
+
+    @Test
+    void testInvertWithZeroSlope() {
+        AffineConverter zeroSlopeConverter = new AffineConverter(0.0, 3.0);
+        assertThrows(AssertionError.class, zeroSlopeConverter::invert, "Invert should throw assertion error when slope is zero");
+    }
+
+    @Test
+    void testCompose() {
+        AffineConverter otherConverter = new AffineConverter(1.0, 2.0);
+        AffineConverter composed = converter.compose(otherConverter);
+
+        assertEquals(7.0, composed.convert(0.0), "Expected composed conversion at 0.0");
+        assertEquals(9.0, composed.convert(1.0), "Expected composed conversion at 1.0");
+        assertEquals(11.0, composed.convert(2.0), "Expected composed conversion at 2.0");
+    }
+}