feat: test coverage implementation of Base64Test.java

Author: NithinU2802

src/test/java/com/thealgorithms/conversions/Base64Test.java

@@ -0,0 +1,203 @@
+package com.thealgorithms.conversions;
+
+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.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+/**
+ * Test cases for Base64 encoding and decoding.
+ * 
+ * Author: Nithin U.
+ * Github: https://github.com/NithinU2802
+ */
+
+class Base64Test {
+
+    @Test
+    void testBase64Alphabet() {
+        // Test that all Base64 characters are handled correctly
+        String allChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+        String encoded = Base64.encode(allChars);
+        String decoded = Base64.decodeToString(encoded);
+        assertEquals(allChars, decoded);
+    }
+
+    @ParameterizedTest
+    @CsvSource({
+        "'', ''",
+        "A, QQ==",
+        "AB, QUI=",
+        "ABC, QUJD",
+        "ABCD, QUJDRA==",
+        "Hello, SGVsbG8=",
+        "'Hello World', SGVsbG8gV29ybGQ=",
+        "'Hello, World!', 'SGVsbG8sIFdvcmxkIQ=='",
+        "'The quick brown fox jumps over the lazy dog', 'VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZw=='",
+        "123456789, MTIzNDU2Nzg5",
+        "'Base64 encoding test', 'QmFzZTY0IGVuY29kaW5nIHRlc3Q='"
+    })
+    void testStringEncoding(String input, String expected) {
+        assertEquals(expected, Base64.encode(input));
+    }
+
+    @ParameterizedTest
+    @CsvSource({
+        "'', ''",
+        "QQ==, A",
+        "QUI=, AB", 
+        "QUJD, ABC",
+        "QUJDRA==, ABCD",
+        "SGVsbG8=, Hello",
+        "'SGVsbG8gV29ybGQ=', 'Hello World'",
+        "'SGVsbG8sIFdvcmxkIQ==', 'Hello, World!'",
+        "'VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZw==', 'The quick brown fox jumps over the lazy dog'",
+        "MTIzNDU2Nzg5, 123456789",
+        "'QmFzZTY0IGVuY29kaW5nIHRlc3Q=', 'Base64 encoding test'"
+    })
+    void testStringDecoding(String input, String expected) {
+        assertEquals(expected, Base64.decodeToString(input));
+    }
+
+    @Test
+    void testByteArrayEncoding() {
+        byte[] input = {72, 101, 108, 108, 111};
+        String expected = "SGVsbG8=";
+        assertEquals(expected, Base64.encode(input));
+    }
+
+    @Test
+    void testByteArrayDecoding() {
+        String input = "SGVsbG8=";
+        byte[] expected = {72, 101, 108, 108, 111};
+        assertArrayEquals(expected, Base64.decode(input));
+    }
+
+    @Test
+    void testRoundTripEncoding() {
+        String[] testStrings = {
+            "",
+            "A",
+            "AB", 
+            "ABC",
+            "Hello, World!",
+            "The quick brown fox jumps over the lazy dog",
+            "1234567890",
+            "Special chars: !@#$%^&*()_+-=[]{}|;:,.<>?",
+            "Unicode: வணக்கம்", // Tamil for "Hello"
+            "Multi-line\nstring\rwith\tdifferent\nwhitespace"
+        };
+
+        for (String original : testStrings) {
+            String encoded = Base64.encode(original);
+            String decoded = Base64.decodeToString(encoded);
+            assertEquals(original, decoded, "Round trip failed for: " + original);
+        }
+    }
+
+    @Test
+    void testRoundTripByteArrayEncoding() {
+        byte[][] testArrays = {
+            {},
+            {0},
+            {-1},
+            {0, 1, 2, 3, 4, 5},
+            {-128, -1, 0, 1, 127},
+            {72, 101, 108, 108, 111, 44, 32, 87, 111, 114, 108, 100, 33}
+        };
+
+        for (byte[] original : testArrays) {
+            String encoded = Base64.encode(original);
+            byte[] decoded = Base64.decode(encoded);
+            assertArrayEquals(original, decoded, "Round trip failed for byte array");
+        }
+    }
+
+    @Test
+    void testBinaryData() {
+        // Test with binary data that might contain null bytes
+        byte[] binaryData = new byte[256];
+        for (int i = 0; i < 256; i++) {
+            binaryData[i] = (byte) i;
+        }
+        
+        String encoded = Base64.encode(binaryData);
+        byte[] decoded = Base64.decode(encoded);
+        assertArrayEquals(binaryData, decoded);
+    }
+
+    @Test
+    void testNullInputEncoding() {
+        assertThrows(IllegalArgumentException.class, () -> Base64.encode((String) null));
+        assertThrows(IllegalArgumentException.class, () -> Base64.encode((byte[]) null));
+    }
+
+    @Test
+    void testNullInputDecoding() {
+        assertThrows(IllegalArgumentException.class, () -> Base64.decode(null));
+        assertThrows(IllegalArgumentException.class, () -> Base64.decodeToString(null));
+    }
+
+    @Test
+    void testInvalidBase64Characters() {
+        assertThrows(IllegalArgumentException.class, () -> Base64.decode("SGVsbG8@"));
+        assertThrows(IllegalArgumentException.class, () -> Base64.decode("SGVsbG8#"));
+        assertThrows(IllegalArgumentException.class, () -> Base64.decode("SGVsbG8$"));
+        assertThrows(IllegalArgumentException.class, () -> Base64.decode("SGVsbG8%"));
+    }
+
+    @Test
+    void testPaddingVariations() {
+        // Test different padding scenarios '='
+        assertEquals("A", Base64.decodeToString("QQ=="));
+        assertEquals("AB", Base64.decodeToString("QUI="));
+        assertEquals("ABC", Base64.decodeToString("QUJD"));
+    }
+
+    @Test
+    void testPaddingConsistency() {
+        // Ensure that strings requiring different amounts of padding encode/decode correctly
+        String[] testCases = {"A", "AB", "ABC", "ABCD", "ABCDE", "ABCDEF"};
+        
+        for (String test : testCases) {
+            String encoded = Base64.encode(test);
+            String decoded = Base64.decodeToString(encoded);
+            assertEquals(test, decoded);
+            
+            // Verify padding is correct
+            int expectedPadding = (3 - (test.length() % 3)) % 3;
+            int actualPadding = 0;
+            for (int i = encoded.length() - 1; i >= 0 && encoded.charAt(i) == '='; i--) {
+                actualPadding++;
+            }
+            assertEquals(expectedPadding, actualPadding, "Incorrect padding for: " + test);
+        }
+    }
+
+    @Test
+    void testLargeData() {
+        // Test with larger data to ensure scalability
+        StringBuilder largeString = new StringBuilder();
+        for (int i = 0; i < 1000; i++) {
+            largeString.append("This is a test string for Base64 encoding. ");
+        }
+        
+        String original = largeString.toString();
+        String encoded = Base64.encode(original);
+        String decoded = Base64.decodeToString(encoded);
+        assertEquals(original, decoded);
+    }
+
+    @Test
+    void testEmptyAndSingleCharacter() {
+        // Test edge cases
+        assertEquals("", Base64.encode(""));
+        assertEquals("", Base64.decodeToString(""));
+        
+        assertEquals("QQ==", Base64.encode("A"));
+        assertEquals("A", Base64.decodeToString("QQ=="));
+    }
+
+}