refactor: Enhance docs, add tests in PerlinNoise (#6635)

* refactor: Enhance docs, add tests in `PerlinNoise` * Fix lint * Fix lint --------- Co-authored-by: Deniz Altunkapan <deniz.altunkapan@outlook.com>
2025-12-19 07:00:35 +08:00 · 2025-10-11 18:45:18 +05:30
parent 69d8406a6b
commit f0fb971f35
2 changed files with 208 additions and 43 deletions
--- a/src/test/java/com/thealgorithms/others/PerlinNoiseTest.java
+++ b/src/test/java/com/thealgorithms/others/PerlinNoiseTest.java
@@ -0,0 +1,103 @@
+package com.thealgorithms.others;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+class PerlinNoiseTest {
+
+    @Test
+    @DisplayName("generatePerlinNoise returns array with correct dimensions")
+    void testDimensions() {
+        int w = 8;
+        int h = 6;
+        float[][] noise = PerlinNoise.generatePerlinNoise(w, h, 4, 0.6f, 123L);
+        assertThat(noise).hasDimensions(w, h);
+    }
+
+    @Test
+    @DisplayName("All values are within [0,1] after normalization")
+    void testRange() {
+        int w = 16;
+        int h = 16;
+        float[][] noise = PerlinNoise.generatePerlinNoise(w, h, 5, 0.7f, 42L);
+        for (int x = 0; x < w; x++) {
+            for (int y = 0; y < h; y++) {
+                assertThat(noise[x][y]).isBetween(0f, 1f);
+            }
+        }
+    }
+
+    @Test
+    @DisplayName("Deterministic for same parameters and seed")
+    void testDeterminism() {
+        int w = 10;
+        int h = 10;
+        long seed = 98765L;
+        float[][] a = PerlinNoise.generatePerlinNoise(w, h, 3, 0.5f, seed);
+        float[][] b = PerlinNoise.generatePerlinNoise(w, h, 3, 0.5f, seed);
+        for (int x = 0; x < w; x++) {
+            for (int y = 0; y < h; y++) {
+                assertThat(a[x][y]).isEqualTo(b[x][y]);
+            }
+        }
+    }
+
+    @Test
+    @DisplayName("Different seeds produce different outputs (probabilistically)")
+    void testDifferentSeeds() {
+        int w = 12;
+        int h = 12;
+        float[][] a = PerlinNoise.generatePerlinNoise(w, h, 4, 0.8f, 1L);
+        float[][] b = PerlinNoise.generatePerlinNoise(w, h, 4, 0.8f, 2L);
+
+        // Count exact equalities; expect very few or none.
+        int equalCount = 0;
+        for (int x = 0; x < w; x++) {
+            for (int y = 0; y < h; y++) {
+                if (Float.compare(a[x][y], b[x][y]) == 0) {
+                    equalCount++;
+                }
+            }
+        }
+        assertThat(equalCount).isLessThan(w * h / 10); // less than 10% equal exact values
+    }
+
+    @Test
+    @DisplayName("Interpolation endpoints are respected")
+    void testInterpolateEndpoints() {
+        assertThat(PerlinNoise.interpolate(0f, 1f, 0f)).isEqualTo(0f);
+        assertThat(PerlinNoise.interpolate(0f, 1f, 1f)).isEqualTo(1f);
+        assertThat(PerlinNoise.interpolate(0.2f, 0.8f, 0.5f)).isEqualTo(0.5f);
+    }
+
+    @Test
+    @DisplayName("Single octave reduces to bilinear interpolation of base grid")
+    void testSingleOctaveLayer() {
+        int w = 8;
+        int h = 8;
+        long seed = 7L;
+        float[][] base = PerlinNoise.createBaseGrid(w, h, seed);
+        float[][] layer = PerlinNoise.generatePerlinNoiseLayer(base, w, h, 0); // period=1
+        // With period = 1, x0=x, x1=(x+1)%w etc. Values should be smooth and within
+        // [0,1]
+        for (int x = 0; x < w; x++) {
+            for (int y = 0; y < h; y++) {
+                assertThat(layer[x][y]).isBetween(0f, 1f);
+            }
+        }
+    }
+
+    @Test
+    @DisplayName("Invalid inputs are rejected")
+    void testInvalidInputs() {
+        assertThatThrownBy(() -> PerlinNoise.generatePerlinNoise(0, 5, 1, 0.5f, 1L)).isInstanceOf(IllegalArgumentException.class);
+        assertThatThrownBy(() -> PerlinNoise.generatePerlinNoise(5, -1, 1, 0.5f, 1L)).isInstanceOf(IllegalArgumentException.class);
+        assertThatThrownBy(() -> PerlinNoise.generatePerlinNoise(5, 5, 0, 0.5f, 1L)).isInstanceOf(IllegalArgumentException.class);
+        assertThatThrownBy(() -> PerlinNoise.generatePerlinNoise(5, 5, 1, 0f, 1L)).isInstanceOf(IllegalArgumentException.class);
+        assertThatThrownBy(() -> PerlinNoise.generatePerlinNoise(5, 5, 1, Float.NaN, 1L)).isInstanceOf(IllegalArgumentException.class);
+        assertThatThrownBy(() -> PerlinNoise.generatePerlinNoise(5, 5, 1, 1.1f, 1L)).isInstanceOf(IllegalArgumentException.class);
+    }
+}