Fix MiniMaxAlgorithm setScores bug and add comprehensive tests (#6566)

yashsaha555 · sousaha97 · DenizAltunkapan · web-flow · commit 15695c6e549c · 2025-10-02T09:24:25.000+02:00
* Fix MiniMaxAlgorithm setScores bug and add comprehensive tests

- Fix bug in setScores method where scores.length % 1 == 0 always returned true
- Add isPowerOfTwo helper method to properly validate array length
- Add comprehensive unit tests covering edge cases and algorithm correctness
- Tests include validation for power of 2 check, minimax logic, and error handling

Fixes issue with incorrect validation logic in MiniMaxAlgorithm.setScores()

* Fix Checkstyle violations and improve setScores validation

- Replace star imports with explicit imports in test file
- Remove trailing whitespaces from all lines
- Add proper file ending newline
- Improve setScores method to handle edge cases properly
- Use direct bit manipulation for power-of-2 check as suggested
- Ensure error message is printed and scores remain unchanged for invalid input

All Checkstyle violations resolved and tests pass successfully.

* Add missing newline at end of MiniMaxAlgorithmTest.java

- Fix Checkstyle violation: NewlineAtEndOfFile
- Ensure file ends with proper newline character
- All tests continue to pass successfully

* Fix PMD violation by utilizing isPowerOfTwo method

- Replace inline bit manipulation with isPowerOfTwo method call
- Resolves PMD UnusedPrivateMethod violation
- Maintains same validation logic and error handling
- All tests continue to pass successfully

* test: improve MiniMaxAlgorithm test coverage for CodeCov

- Add comprehensive test cases for isPowerOfTwo function edge cases
- Test setScores method with various invalid array lengths (0, 3, 5, 6, 7, 9, 10, 15)
- Add tests for large valid powers of 2 (up to 64 elements)
- Ensure complete coverage of error handling branches
- Increase test count from 14 to 19 tests
- Fix partial coverage issues identified in CodeCov report

Resolves CodeCov coverage gaps in MiniMaxAlgorithm.java

* Fix checkstyle errors

* Fix checkstyle errors

---------

Co-authored-by: ssaha &lt;ssaha@wiley.com&gt;
Co-authored-by: Deniz Altunkapan &lt;93663085+DenizAltunkapan@users.noreply.github.com&gt;
diff --git a/src/main/java/com/thealgorithms/others/MiniMaxAlgorithm.java b/src/main/java/com/thealgorithms/others/MiniMaxAlgorithm.java
@@ -109,13 +109,18 @@ private int log2(int n) {
         return (n == 1) ? 0 : log2(n / 2) + 1;
     }
 
+    // A utility function to check if a number is a power of 2
+    private boolean isPowerOfTwo(int n) {
+        return n > 0 && (n & (n - 1)) == 0;
+    }
+
     public void setScores(int[] scores) {
-        if (scores.length % 1 == 0) {
-            this.scores = scores;
-            height = log2(this.scores.length);
-        } else {
+        if (!isPowerOfTwo(scores.length)) {
             System.out.println("The number of scores must be a power of 2.");
+            return;
         }
+        this.scores = scores;
+        height = log2(this.scores.length);
     }
 
     public int[] getScores() {
diff --git a/src/test/java/com/thealgorithms/others/MiniMaxAlgorithmTest.java b/src/test/java/com/thealgorithms/others/MiniMaxAlgorithmTest.java
@@ -0,0 +1,277 @@
+package com.thealgorithms.others;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test class for MiniMaxAlgorithm
+ * Tests the minimax algorithm implementation for game tree evaluation
+ */
+class MiniMaxAlgorithmTest {
+
+    private MiniMaxAlgorithm miniMax;
+    private final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+    private final PrintStream originalOut = System.out;
+
+    @BeforeEach
+    void setUp() {
+        miniMax = new MiniMaxAlgorithm();
+        System.setOut(new PrintStream(outputStream));
+    }
+
+    @Test
+    void testConstructorCreatesValidScores() {
+        // The default constructor should create scores array of length 8 (2^3)
+        assertEquals(8, miniMax.getScores().length);
+        assertEquals(3, miniMax.getHeight());
+
+        // All scores should be positive (between 1 and 99)
+        for (int score : miniMax.getScores()) {
+            assertTrue(score >= 1 && score <= 99);
+        }
+    }
+
+    @Test
+    void testSetScoresWithValidPowerOfTwo() {
+        int[] validScores = {10, 20, 30, 40};
+        miniMax.setScores(validScores);
+
+        assertArrayEquals(validScores, miniMax.getScores());
+        assertEquals(2, miniMax.getHeight()); // log2(4) = 2
+    }
+
+    @Test
+    void testSetScoresWithInvalidLength() {
+        int[] invalidScores = {10, 20, 30}; // Length 3 is not a power of 2
+        miniMax.setScores(invalidScores);
+
+        // Should print error message and not change the scores
+        String output = outputStream.toString();
+        assertTrue(output.contains("The number of scores must be a power of 2."));
+
+        // Scores should remain unchanged (original length 8)
+        assertEquals(8, miniMax.getScores().length);
+    }
+
+    @Test
+    void testSetScoresWithZeroLength() {
+        int[] emptyScores = {}; // Length 0 is not a power of 2
+        miniMax.setScores(emptyScores);
+
+        // Should print error message and not change the scores
+        String output = outputStream.toString();
+        assertTrue(output.contains("The number of scores must be a power of 2."));
+
+        // Scores should remain unchanged (original length 8)
+        assertEquals(8, miniMax.getScores().length);
+    }
+
+    @Test
+    void testSetScoresWithVariousInvalidLengths() {
+        // Test multiple invalid lengths to ensure isPowerOfTwo function is fully covered
+        int[][] invalidScoreArrays = {
+            {1, 2, 3, 4, 5}, // Length 5
+            {1, 2, 3, 4, 5, 6}, // Length 6
+            {1, 2, 3, 4, 5, 6, 7}, // Length 7
+            new int[9], // Length 9
+            new int[10], // Length 10
+            new int[15] // Length 15
+        };
+
+        for (int[] invalidScores : invalidScoreArrays) {
+            // Clear the output stream for each test
+            outputStream.reset();
+            miniMax.setScores(invalidScores);
+
+            // Should print error message for each invalid length
+            String output = outputStream.toString();
+            assertTrue(output.contains("The number of scores must be a power of 2."), "Failed for array length: " + invalidScores.length);
+        }
+
+        // Scores should remain unchanged (original length 8)
+        assertEquals(8, miniMax.getScores().length);
+    }
+
+    @Test
+    void testSetScoresWithSingleElement() {
+        int[] singleScore = {42};
+        miniMax.setScores(singleScore);
+
+        assertArrayEquals(singleScore, miniMax.getScores());
+        assertEquals(0, miniMax.getHeight()); // log2(1) = 0
+    }
+
+    @Test
+    void testMiniMaxWithKnownScores() {
+        // Test with a known game tree: [3, 12, 8, 2]
+        int[] testScores = {3, 12, 8, 2};
+        miniMax.setScores(testScores);
+
+        // Maximizer starts: should choose max(min(3,12), min(8,2)) = max(3, 2) = 3
+        int result = miniMax.miniMax(0, true, 0, false);
+        assertEquals(3, result);
+    }
+
+    @Test
+    void testMiniMaxWithMinimizerFirst() {
+        // Test with minimizer starting first
+        int[] testScores = {3, 12, 8, 2};
+        miniMax.setScores(testScores);
+
+        // Minimizer starts: should choose min(max(3,12), max(8,2)) = min(12, 8) = 8
+        int result = miniMax.miniMax(0, false, 0, false);
+        assertEquals(8, result);
+    }
+
+    @Test
+    void testMiniMaxWithLargerTree() {
+        // Test with 8 elements: [5, 6, 7, 4, 5, 3, 6, 2]
+        int[] testScores = {5, 6, 7, 4, 5, 3, 6, 2};
+        miniMax.setScores(testScores);
+
+        // Maximizer starts
+        int result = miniMax.miniMax(0, true, 0, false);
+        // Expected: max(min(max(5,6), max(7,4)), min(max(5,3), max(6,2)))
+        //         = max(min(6, 7), min(5, 6)) = max(6, 5) = 6
+        assertEquals(6, result);
+    }
+
+    @Test
+    void testMiniMaxVerboseOutput() {
+        int[] testScores = {3, 12, 8, 2};
+        miniMax.setScores(testScores);
+
+        miniMax.miniMax(0, true, 0, true);
+
+        String output = outputStream.toString();
+        assertTrue(output.contains("Maximizer"));
+        assertTrue(output.contains("Minimizer"));
+        assertTrue(output.contains("chooses"));
+    }
+
+    @Test
+    void testGetRandomScoresLength() {
+        int[] randomScores = MiniMaxAlgorithm.getRandomScores(4, 50);
+        assertEquals(16, randomScores.length); // 2^4 = 16
+
+        // All scores should be between 1 and 50
+        for (int score : randomScores) {
+            assertTrue(score >= 1 && score <= 50);
+        }
+    }
+
+    @Test
+    void testGetRandomScoresWithDifferentParameters() {
+        int[] randomScores = MiniMaxAlgorithm.getRandomScores(2, 10);
+        assertEquals(4, randomScores.length); // 2^2 = 4
+
+        // All scores should be between 1 and 10
+        for (int score : randomScores) {
+            assertTrue(score >= 1 && score <= 10);
+        }
+    }
+
+    @Test
+    void testMainMethod() {
+        // Test that main method runs without errors
+        assertDoesNotThrow(() -> MiniMaxAlgorithm.main(new String[] {}));
+
+        String output = outputStream.toString();
+        assertTrue(output.contains("The best score for"));
+        assertTrue(output.contains("Maximizer"));
+    }
+
+    @Test
+    void testHeightCalculation() {
+        // Test height calculation for different array sizes
+        int[] scores2 = {1, 2};
+        miniMax.setScores(scores2);
+        assertEquals(1, miniMax.getHeight()); // log2(2) = 1
+
+        int[] scores16 = new int[16];
+        miniMax.setScores(scores16);
+        assertEquals(4, miniMax.getHeight()); // log2(16) = 4
+    }
+
+    @Test
+    void testEdgeCaseWithZeroScores() {
+        int[] zeroScores = {0, 0, 0, 0};
+        miniMax.setScores(zeroScores);
+
+        int result = miniMax.miniMax(0, true, 0, false);
+        assertEquals(0, result);
+    }
+
+    @Test
+    void testEdgeCaseWithNegativeScores() {
+        int[] negativeScores = {-5, -2, -8, -1};
+        miniMax.setScores(negativeScores);
+
+        // Tree evaluation with maximizer first:
+        // Level 1 (minimizer): min(-5,-2) = -5, min(-8,-1) = -8
+        // Level 0 (maximizer): max(-5, -8) = -5
+        int result = miniMax.miniMax(0, true, 0, false);
+        assertEquals(-5, result);
+    }
+
+    void tearDown() {
+        System.setOut(originalOut);
+    }
+
+    @Test
+    void testSetScoresWithNegativeLength() {
+        // This test ensures the first condition of isPowerOfTwo (n > 0) is tested
+        // Although we can't directly create an array with negative length,
+        // we can test edge cases around zero and ensure proper validation
+
+        // Test with array length 0 (edge case for n > 0 condition)
+        int[] emptyArray = new int[0];
+        outputStream.reset();
+        miniMax.setScores(emptyArray);
+
+        String output = outputStream.toString();
+        assertTrue(output.contains("The number of scores must be a power of 2."));
+        assertEquals(8, miniMax.getScores().length); // Should remain unchanged
+    }
+
+    @Test
+    void testSetScoresWithLargePowerOfTwo() {
+        // Test with a large power of 2 to ensure the algorithm works correctly
+        int[] largeValidScores = new int[32]; // 32 = 2^5
+        for (int i = 0; i < largeValidScores.length; i++) {
+            largeValidScores[i] = i + 1;
+        }
+
+        miniMax.setScores(largeValidScores);
+        assertArrayEquals(largeValidScores, miniMax.getScores());
+        assertEquals(5, miniMax.getHeight()); // log2(32) = 5
+    }
+
+    @Test
+    void testSetScoresValidEdgeCases() {
+        // Test valid powers of 2 to ensure isPowerOfTwo returns true correctly
+        int[][] validPowersOf2 = {
+            new int[1], // 1 = 2^0
+            new int[2], // 2 = 2^1
+            new int[4], // 4 = 2^2
+            new int[8], // 8 = 2^3
+            new int[16], // 16 = 2^4
+            new int[64] // 64 = 2^6
+        };
+
+        int[] expectedHeights = {0, 1, 2, 3, 4, 6};
+
+        for (int i = 0; i < validPowersOf2.length; i++) {
+            miniMax.setScores(validPowersOf2[i]);
+            assertEquals(validPowersOf2[i].length, miniMax.getScores().length, "Failed for array length: " + validPowersOf2[i].length);
+            assertEquals(expectedHeights[i], miniMax.getHeight(), "Height calculation failed for array length: " + validPowersOf2[i].length);
+        }
+    }
+}
