Refactored tests of the Permutation class (suggestion of Sonatype Lift's technical debt scan)

src/test/java/org/cicirello/permutations/PermutationConstructorRelatedTests.java

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+/*
+ * JavaPermutationTools: A Java library for computation on permutations and sequences
+ * Copyright 2005-2022 Vincent A. Cicirello, <https://www.cicirello.org/>.
+ *
+ * This file is part of JavaPermutationTools (https://jpt.cicirello.org/).
+ *
+ * JavaPermutationTools is free software: you can 
+ * redistribute it and/or modify it under the terms of the GNU 
+ * General Public License as published by the Free Software 
+ * Foundation, either version 3 of the License, or (at your 
+ * option) any later version.
+ *
+ * JavaPermutationTools is distributed in the hope 
+ * that it will be useful, but WITHOUT ANY WARRANTY; without even 
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A 
+ * PARTICULAR PURPOSE.  See the GNU General Public License for more 
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with JavaPermutationTools.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.cicirello.permutations;
+
+import java.util.SplittableRandom;
+import java.util.Random;
+import java.math.BigInteger;
+import org.junit.jupiter.api.*;
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * JUnit tests for the constructors and methods of the Permutation class.
+ */
+public class PermutationConstructorRelatedTests extends SharedTestHelpersPermutation {
+
+	// Set to false to enable chi square tests for randomness of constructor and
+	// scramble, specifically for the constructor and scramble that uses ThreadLocalRandom
+	// since it is not seedable.  Tests passed repeatedly as of last update.
+	// If that constructor or scramble is updated, then this flag should be set false to enable
+	// tests (and reset true after passing).
+	// Note: This doesn't disable those tests for the constructors/scramble methods
+	// that use a source of randomness that is seedable.
+	private static final boolean disableChiSquareTests = true;
+
+	@Test
+	public void testZeroLengthPermutations() {
+		// different ways of constructing 0 length permutations.
+		Permutation p1 = new Permutation(0);		
+		Permutation p2 = new Permutation(new int[] {});
+		Permutation p3 = new Permutation(0,0);
+		Permutation copy = new Permutation(p1);
+
+		// the above 4 should all be equivalent, so check
+		assertEquals(p1,p2);
+		assertEquals(p1,p3);
+		assertEquals(p1,copy);
+		assertEquals(p2,p3);
+		assertEquals(p2,copy);
+		assertEquals(p3,copy);
+	}
+
+	@Test
+	public void testPermutationConstructor() {
+		for (int n = 1; n <= 10; n++) {
+			for (int i = 0; i < 10; i++) {
+				Permutation p = new Permutation(n);
+				validatePermutation(p, n);
+			}
+		}
+		SplittableRandom r = new SplittableRandom();
+		for (int n = 1; n <= 10; n++) {
+			for (int i = 0; i < 10; i++) {
+				Permutation p = new Permutation(n, r);
+				validatePermutation(p, n);
+			}
+		}
+	}
+
+	@Test
+	public void testPermutationConstructorSpecific() {
+		int fact = 1;
+		for (int n = 1; n <= 6; n++) {
+			fact *= n;
+			for (int i = 0; i < fact; i++) {
+				Permutation p = new Permutation(n, i);
+				assertEquals(i, p.toInteger());
+				assertEquals(BigInteger.valueOf(i), p.toBigInteger());
+				validatePermutation(p, n);
+			}
+		}
+		int n = 12;
+		fact = 1;
+		for (int i = 2; i <= n; i++) {
+			fact *= i;
+		}
+		SplittableRandom r = new SplittableRandom();
+		for (int i = 0; i < 100; i++) {
+			int which = r.nextInt(fact);
+			Permutation p = new Permutation(n, which);
+			assertEquals(which, p.toInteger());
+			assertEquals(BigInteger.valueOf(which), p.toBigInteger());
+			validatePermutation(p, n);
+		}
+	}
+
+	@Test
+	public void testPermutationConstructorSpecificBigInt() {
+		int fact = 1;
+		for (int n = 1; n <= 6; n++) {
+			fact *= n;
+			for (int i = 0; i < fact; i++) {
+				BigInteger big = BigInteger.valueOf(i);
+				Permutation p = new Permutation(n, big);
+				assertEquals(i, p.toInteger());
+				assertEquals(big, p.toBigInteger());
+				validatePermutation(p, n);
+			}
+		}
+		int n = 12;
+		fact = 1;
+		for (int i = 2; i <= n; i++) {
+			fact *= i;
+		}
+		SplittableRandom r = new SplittableRandom();
+		for (int i = 0; i < 100; i++) {
+			int which = r.nextInt(fact);
+			BigInteger bigWhich = BigInteger.valueOf(which);
+			Permutation p = new Permutation(n, bigWhich);
+			assertEquals(which, p.toInteger());
+			assertEquals(bigWhich, p.toBigInteger());
+			validatePermutation(p, n);
+		}
+		n = 20;
+		BigInteger f = BigInteger.ONE;
+		for (int i = 2; i <= n; i++) {
+			f = f.multiply(BigInteger.valueOf(i));
+		}
+		for (int i = 0; i < 20; i++) {
+			BigInteger bigWhich = new BigInteger(f.bitLength()-1, new Random(42));
+			Permutation p = new Permutation(n, bigWhich);
+			assertEquals(bigWhich, p.toBigInteger());
+			validatePermutation(p, n);
+		}
+	}
+
+	@Test
+	public void testToIntegerExceptions() {
+		UnsupportedOperationException thrown = assertThrows( 
+			UnsupportedOperationException.class,
+			() -> (new Permutation(13)).toInteger()
+		);
+	}
+
+	@Test
+	public void testPermutationCopyConstructor() {
+		for (int n = 1; n <= 10; n++) {
+			for (int i = 0; i < 10; i++) {
+				Permutation p = new Permutation(n);
+				Permutation copy = new Permutation(p);
+				assertEquals(p, copy);
+				assertEquals(p.hashCode(), copy.hashCode());
+			}
+		}
+	}
+
+	@Test
+	public void testPermutationCopyMethod() {
+		for (int n = 1; n <= 10; n++) {
+			for (int i = 0; i < 10; i++) {
+				Permutation p = new Permutation(n);
+				Permutation copy = p.copy();
+				assertEquals(p, copy);
+				assertTrue(p != copy);
+				assertEquals(p.hashCode(), copy.hashCode());
+			}
+		}
+	}
+
+	@Test
+	public void testPermutationEqualsSpecialCases() {
+		Permutation p = new Permutation(5);
+		assertTrue(p.equals(p));
+		assertFalse(p.equals(null));
+		assertFalse(p.equals("hello"));
+	}
+
+	@Test
+	public void testPermutationConstructorCopyPartial() {
+		for (int n = 1; n <= 10; n++) {
+			int[] forward = new int[n];
+			int[] backward = new int[n];
+			for (int i = 0; i < n; i++) {
+				backward[n-1-i] = forward[i] = i;
+			}
+			Permutation p1 = new Permutation(forward);
+			Permutation p2 = new Permutation(backward);
+			for (int m = 0; m <= n; m++) {
+				Permutation copy1 = new Permutation(p1, m);
+				Permutation copy2 = new Permutation(p2, m);
+				assertEquals(m, copy1.length());
+				assertEquals(m, copy2.length());
+				validatePermutation(copy1, m);
+				validatePermutation(copy2, m);
+				for (int i = 0; i < m; i++) {
+					assertEquals(i, copy1.get(i));
+					assertEquals(m-1-i, copy2.get(i));
+				}
+			}
+		}
+	}
+
+	@Test
+	public void testPermutationEquals() {
+		Permutation p = new Permutation(10);
+		for (int n = 1; n < 10; n++) {
+			Permutation partialCopy = new Permutation(p, n);
+			assertNotEquals(p, partialCopy);
+		}
+		Permutation copy = new Permutation(p);
+		assertEquals(p, copy);
+		assertNotEquals(new Permutation(new int[] {0, 1, 2, 3}), new Permutation(new int[] {3, 1, 2, 0}));
+	}
+
+	@Test
+	public void testUniformityOfConstructors() {
+		final int N = 12000;
+		SplittableRandom r2 = new SplittableRandom(42);
+		int tooHigh0 = 0;
+		int tooHigh2 = 0;
+		for (int k = 0; k < 100; k++) {
+			int[] counts0 = new int[120];
+			int[] counts2 = new int[120];
+			for (int i = 0; i < N; i++) {
+				Permutation p0 = new Permutation(5);
+				Permutation p2 = new Permutation(5, r2);
+				int j0 = p0.toInteger();
+				int j2 = p2.toInteger();
+				counts0[j0]++;
+				counts2[j2]++;
+			}
+			if (chiSquare(counts0) > 146.567) tooHigh0++;
+			if (chiSquare(counts2) > 146.567) tooHigh2++;
+		}
+		if (!disableChiSquareTests) {
+			assertTrue(tooHigh0 <= 10);
+		}
+		assertTrue(tooHigh2 <= 10);
+	}
+}