diff --git a/src/price/Sums.php b/src/price/Sums.php
index 493444d8..2dd6da7a 100644
--- a/src/price/Sums.php
+++ b/src/price/Sums.php
@@ -5,24 +5,30 @@
 final readonly class Sums implements \JsonSerializable
 {
     /**
-     * @param int[]|null $values quantity => total sum for the quantity
-     * Quantity of what?
-     * Sum of what?
-     * If you know answers please write in the comment
+     * @param array<int, float|int>|null $quantityToSumMap An associative array where:
+     *   - The key represents the **quantity** of the action being charged for
+     *     (e.g., the number of years for an SSL certificate).
+     *   - The value represents the **total sum** or **price** for the given quantity.
+     *
+     * Example (If used to denote bulk prices):
+     * E.g. when you buy an SSL certificate for 1 year – it costs 10$
+     * But for 2 years you pay 15$.
+     *
+     * It will be is stored as
+     *
+     * [1 => 10, 2 => 15]
      */
-    public function __construct(private ?array $values)
+    public function __construct(private ?array $quantityToSumMap)
     {
-        if (!empty($this->values)) {
-            $this->validate($this->values);
-        }
+        $this->validateSums($this->quantityToSumMap);
     }
 
-    private function validate(array $sums): void
+    private function validateSums(?array $sums): void
     {
-        if ($sums) {
+        if (!empty($sums)) {
             foreach ($sums as $value) {
                 if (!is_numeric($value)) {
-                    throw new PriceInvalidArgumentException('Invalid value for sums parameter');
+                    throw new PriceInvalidArgumentException('All sums must be numeric values.');
                 }
             }
         }
@@ -30,21 +36,25 @@ private function validate(array $sums): void
 
     public function values(): ?array
     {
-        return $this->values;
+        return $this->quantityToSumMap;
     }
 
     public function getSum(int $quantity)
     {
-        return $this->values[$quantity] ?? null;
+        return $this->quantityToSumMap[$quantity] ?? null;
     }
 
-    public function getMinSum(): int|string
+    public function getMinSum()
     {
-        return min($this->values);
+        if (empty($this->quantityToSumMap)) {
+            return null;
+        }
+
+        return min($this->quantityToSumMap);
     }
 
     public function jsonSerialize(): ?array
     {
-        return $this->values;
+        return $this->quantityToSumMap;
     }
 }
diff --git a/tests/unit/price/SumsTest.php b/tests/unit/price/SumsTest.php
new file mode 100644
index 00000000..1e17ded3
--- /dev/null
+++ b/tests/unit/price/SumsTest.php
@@ -0,0 +1,96 @@
+<?php declare(strict_types=1);
+
+namespace hiqdev\php\billing\tests\unit\price;
+
+use hiqdev\php\billing\price\PriceInvalidArgumentException;
+use hiqdev\php\billing\price\Sums;
+use JsonSerializable;
+use PHPUnit\Framework\TestCase;
+
+class SumsTest extends TestCase
+{
+    public function testConstructorWithValidData(): void
+    {
+        $validSums = [1 => 10.5, 2 => 15.0, 3 => 20];
+
+        $sums = new Sums($validSums);
+
+        $this->assertSame($validSums, $sums->values());
+    }
+
+    public function testConstructorWithInvalidDataThrowsException(): void
+    {
+        $this->expectException(PriceInvalidArgumentException::class);
+        $this->expectExceptionMessage('All sums must be numeric values.');
+
+        $invalidSums = [1 => 10, 2 => 'abc'];
+
+        new Sums($invalidSums);
+    }
+
+    public function testGetSum(): void
+    {
+        $sums = new Sums([1 => 10, 2 => 15, 3 => 20]);
+
+        $this->assertSame(10, $sums->getSum(1));
+        $this->assertSame(15, $sums->getSum(2));
+        $this->assertNull($sums->getSum(4));  // Not found
+    }
+
+    /**
+     * @dataProvider minSumDataProvider
+     */
+    public function testGetMinSum($input, $expected): void
+    {
+        $sums = new Sums($input);
+
+        $this->assertSame($expected, $sums->getMinSum());
+    }
+
+    public function minSumDataProvider(): array
+    {
+        return [
+            // Single element case
+            'single positive integer' => [[1 => 10], 10],
+            'single negative integer' => [[1 => -10], -10],
+            'single decimal' => [[1 => 5.5], 5.5],
+
+            // Multiple elements case
+            'multiple positive integers' => [[1 => 10, 2 => 20, 3 => 5], 5],
+            'multiple with negative integers' => [[1 => -10, 2 => 20, 3 => 0], -10],
+            'multiple decimals' => [[1 => 10.5, 2 => 20.7, 3 => 5.5], 5.5],
+            'mixed integers and decimals' => [[1 => 10, 2 => 20.7, 3 => 5], 5],
+
+            // Edge cases
+            'positive and negative decimals' => [[1 => -1.5, 2 => 1.5], -1.5],
+            'zero and positive integers' => [[1 => 0, 2 => 5], 0],
+            'zero and negative integers' => [[1 => 0, 2 => -5], -5],
+        ];
+    }
+
+    public function testJsonSerializableBehavior(): void
+    {
+        $sums = new Sums([1 => 10, 2 => 15, 3 => 20]);
+
+        $this->assertInstanceOf(JsonSerializable::class, $sums);
+
+        $expectedJson = json_encode([1 => 10, 2 => 15, 3 => 20]);
+        $this->assertSame($expectedJson, json_encode($sums));
+    }
+
+    public function testSumsWithNullInput(): void
+    {
+        $sums = new Sums(null);
+
+        $this->assertNull($sums->values());
+        $this->assertNull($sums->getSum(1));
+    }
+
+    public function testSumsWithEmptyArray(): void
+    {
+        $sums = new Sums([]);
+
+        $this->assertSame([], $sums->values());
+        $this->assertNull($sums->getSum(1));
+    }
+}
\ No newline at end of file