Add test, Disable TREND_BEST_FIT, POLYNOMIAL_BEST_FIT

src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php

@@ -3,11 +3,14 @@
 namespace PhpOffice\PhpSpreadsheet\Shared\Trend;
 
 use Matrix\Matrix;
+use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
 
 // Phpstan and Scrutinizer seem to have legitimate complaints.
 // $this->slope is specified where an array is expected in several places.
 // But it seems that it should always be float.
 // This code is probably not exercised at all in unit tests.
+// Private bool property $implemented is set to indicate
+//     whether this implementation is correct.
 class PolynomialBestFit extends BestFit
 {
     /**
@@ -21,6 +24,8 @@ class PolynomialBestFit extends BestFit
      */
     protected int $order = 0;
 
+    private bool $implemented = false;
+
     /**
      * Return the order of this polynomial.
      */
@@ -187,6 +192,10 @@ class PolynomialBestFit extends BestFit
      */
     public function __construct(int $order, array $yValues, array $xValues = [])
     {
+        if (!$this->implemented) {
+            throw new SpreadsheetException('Polynomial Best Fit not yet implemented');
+        }
+
         parent::__construct($yValues, $xValues);
 
         if (!$this->error) {

src/PhpSpreadsheet/Shared/Trend/Trend.php

@@ -18,10 +18,8 @@ class Trend
 
     /**
      * Names of the best-fit Trend analysis methods.
-     *
-     * @var string[]
      */
-    private static array $trendTypes = [
+    private const TREND_TYPES = [
         self::TREND_LINEAR,
         self::TREND_LOGARITHMIC,
         self::TREND_EXPONENTIAL,
@@ -93,13 +91,12 @@ class Trend
                 //    Start by generating an instance of each available Trend method
                 $bestFit = [];
                 $bestFitValue = [];
-                foreach (self::$trendTypes as $trendMethod) {
+                foreach (self::TREND_TYPES as $trendMethod) {
                     $className = '\PhpOffice\PhpSpreadsheet\Shared\Trend\\' . $trendMethod . 'BestFit';
-                    //* @phpstan-ignore-next-line
                     $bestFit[$trendMethod] = new $className($yValues, $xValues, $const);
                     $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
                 }
-                if ($trendType != self::TREND_BEST_FIT_NO_POLY) {
+                if ($trendType !== self::TREND_BEST_FIT_NO_POLY) {
                     foreach (self::$trendTypePolynomialOrders as $trendMethod) {
                         $order = (int) substr($trendMethod, -1);
                         $bestFit[$trendMethod] = new PolynomialBestFit($order, $yValues, $xValues);

tests/PhpSpreadsheetTests/Shared/Trend/BestFitTest.php

@@ -0,0 +1,72 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Shared\Trend;
+
+use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
+use PhpOffice\PhpSpreadsheet\Shared\Trend\Trend;
+use PHPUnit\Framework\TestCase;
+
+class BestFitTest extends TestCase
+{
+    private const LBF_PRECISION = 1.0E-4;
+
+    public function testBestFit(): void
+    {
+        $xValues = [45, 55, 47, 75, 90, 100, 100, 95, 88, 50, 45, 58];
+        $yValues = [15, 25, 17, 30, 41, 47, 50, 46, 37, 22, 20, 26];
+        $maxGoodness = -1000.0;
+        $maxType = '';
+
+        $type = Trend::TREND_LINEAR;
+        $result = Trend::calculate($type, $yValues, $xValues);
+        $goodness = $result->getGoodnessOfFit();
+        if ($maxGoodness < $goodness) {
+            $maxGoodness = $goodness;
+            $maxType = $type;
+        }
+        self::assertEqualsWithDelta(0.9628, $goodness, self::LBF_PRECISION);
+
+        $type = Trend::TREND_EXPONENTIAL;
+        $result = Trend::calculate($type, $yValues, $xValues);
+        $goodness = $result->getGoodnessOfFit();
+        if ($maxGoodness < $goodness) {
+            $maxGoodness = $goodness;
+            $maxType = $type;
+        }
+        self::assertEqualsWithDelta(0.9952, $goodness, self::LBF_PRECISION);
+
+        $type = Trend::TREND_LOGARITHMIC;
+        $result = Trend::calculate($type, $yValues, $xValues);
+        $goodness = $result->getGoodnessOfFit();
+        if ($maxGoodness < $goodness) {
+            $maxGoodness = $goodness;
+            $maxType = $type;
+        }
+        self::assertEqualsWithDelta(-0.0724, $goodness, self::LBF_PRECISION);
+
+        $type = Trend::TREND_POWER;
+        $result = Trend::calculate($type, $yValues, $xValues);
+        $goodness = $result->getGoodnessOfFit();
+        if ($maxGoodness < $goodness) {
+            $maxGoodness = $goodness;
+            $maxType = $type;
+        }
+        self::assertEqualsWithDelta(0.9946, $goodness, self::LBF_PRECISION);
+
+        $type = Trend::TREND_BEST_FIT_NO_POLY;
+        $result = Trend::calculate($type, $yValues, $xValues);
+        $goodness = $result->getGoodnessOfFit();
+        self::assertSame($maxGoodness, $goodness);
+        self::assertSame(lcfirst($maxType), $result->getBestFitType());
+
+        try {
+            $type = Trend::TREND_BEST_FIT;
+            $result = Trend::calculate($type, $yValues, $xValues);
+            self::fail('should have failed - TREND_BEST_FIT includes polynomials which are not implemented yet');
+        } catch (SpreadsheetException $e) {
+            self::assertStringContainsString('not yet implemented', $e->getMessage());
+        }
+    }
+}