Fine tuning parameter types in tests

Author: roberto-butti

src/Stat.php

@@ -677,7 +677,7 @@ private static function ranks(array $data): array
             $indexed[] = [$data[$i], $i];
         }
 
-        usort($indexed, fn ($a, $b) => $a[0] <=> $b[0]);
+        usort($indexed, fn(array $a, array $b): int => $a[0] <=> $b[0]);
 
         $ranks = array_fill(0, $n, 0.0);
         $i = 0;

tests/StatTest.php

@@ -403,13 +403,15 @@ public function test_calculates_spearman_correlation_planets(): void
 
         // Linear (Pearson) correlation is imperfect
         $correlation = Stat::correlation($orbitalPeriod, $distFromSun);
+        $this->assertIsFloat($correlation);
         $this->assertEquals(0.9882, round($correlation, 4));
 
         // Kepler's third law: linear correlation between
         // the square of the period and the cube of the distance
-        $periodSquared = array_map(fn ($p) => $p * $p, $orbitalPeriod);
-        $distCubed = array_map(fn ($d) => $d * $d * $d, $distFromSun);
+        $periodSquared = array_map(fn(int $p): int => $p * $p, $orbitalPeriod);
+        $distCubed = array_map(fn(int $d): int => $d * $d * $d, $distFromSun);
         $correlation = Stat::correlation($periodSquared, $distCubed);
+        $this->assertIsFloat($correlation);
         $this->assertEquals(1.0, round($correlation, 4));
     }