add a logarithm expectation

README.md

@@ -79,3 +79,12 @@ $$\mid -3 \mid$$
     expect(3)->toBeAbsoluteOf(-3);
     expect(-3)->not->toBeAbsoluteOf(-3);
 ```
+
+#### `toBeLogarithmOf()`
+$$\log_{base}(number)$$
+<br>
+Base default is euler's number.
+```php
+    expect(0.69897000433602)->toBeLogarithmOf(number: 5, base: 10);
+    expect(1)->not->toBeLogarithmOf(number: 1);
+```

src/Expectation.php

@@ -128,6 +128,16 @@ public function toBeFactorialOf(int $number): PestExpectation
         return expect($this->value === $factorial)->toBeTrue();
     }
 
+    /**
+     * @return PestExpectation<TValue>
+     */
+    public function toBeLogarithmOf(float $number, float $base = M_E): PestExpectation
+    {
+        return expect($base > 0)->toBeTrue('The base must be greater than 0')
+            ->and($number > 0)->toBeTrue('The number must be greater than 0')
+            ->and((string) $this->value === (string) log($number, $base))->toBeTrue("$this->value doesn't equal log($number, $base)");
+    }
+
     /**
      * @return PestExpectation<TValue>
      */

tests/toBeLogarithmOf.php

@@ -0,0 +1,31 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+it('passes', function (int|float $value, float $number, float $base): void {
+    expect($value)->toBeLogarithmOf($number, $base);
+})->with([
+    [1.6094379124341, 5, M_E],
+    [2.302585092994, 10, M_E],
+    [-3.5849625007212, 12, .5],
+]);
+
+it('passes not', function (float $number, float $base): void {
+    expect(1)->not->toBeLogarithmOf($number, $base);
+})->with([
+    [5, M_E],
+    [10, M_E],
+    [12, .5],
+]);
+
+test('failures', function (float $number, float $base): void {
+    expect(1)->toBeLogarithmOf($number, $base);
+})->with([
+    [1, M_E],
+    [-1, M_E],
+    [1, -M_E],
+])->throws(ExpectationFailedException::class);
+
+test('failures not', function (): void {
+    expect(0)->not->toBeLogarithmOf(1);
+})->throws(ExpectationFailedException::class);