diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2a9ab91..dc79a55 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -11,6 +11,9 @@ jobs:
             - name: Checkout
               uses: actions/checkout@v1
 
+            - name: Build docker image
+              run: USER_ID=$(stat -c %u .) GROUP_ID=$(stat -c %g .) ./docker-dev build dev
+
             - name: Install dependencies
               run: ./docker-dev run --rm dev composer install
 
diff --git a/src/Serialization/BinaryEncoder.php b/src/Serialization/BinaryEncoder.php
index 17dfa6c..ee708ee 100644
--- a/src/Serialization/BinaryEncoder.php
+++ b/src/Serialization/BinaryEncoder.php
@@ -34,13 +34,25 @@ public function encodeDouble(float $double): string
 
     private function encodeLong(int $value): string
     {
-        $n = ($value << 1) ^ ($value >> 63);
-        $str = '';
-        while (0 != ($n & ~0x7F)) {
-            $str .= chr(($n & 0x7F) | 0x80);
-            $n >>= 7;
+        $n = (int) $value;
+        $n = ($n << 1) ^ ($n >> 63);
+
+        if ($n >= 0 && $n < 0x80) {
+            return chr($n);
         }
-        $str .= chr($n);
-        return $str;
+
+        $buf = [];
+        if (($n & ~0x7F) != 0) {
+            $buf[] = ($n | 0x80) & 0xFF;
+            $n = ($n >> 7) ^ (($n >> 63) << 57); // unsigned shift right ($n >>> 7)
+
+            while ($n > 0x7F) {
+                $buf[] = ($n | 0x80) & 0xFF;
+                $n >>= 7; // $n is always positive here
+            }
+        }
+
+        $buf[] = $n;
+        return pack('C*', ...$buf);
     }
 }
diff --git a/tests/Unit/Deserialization/BinaryDecoderTest.php b/tests/Unit/Deserialization/BinaryDecoderTest.php
index 50a310b..630ed49 100644
--- a/tests/Unit/Deserialization/BinaryDecoderTest.php
+++ b/tests/Unit/Deserialization/BinaryDecoderTest.php
@@ -61,7 +61,7 @@ public function testSkipLongWithMultipleBytes(): void
     public function testReadFloatWithValidValue(): void
     {
         // Test reading a float value (3.14)
-        $floatBytes = pack('g', 3.14);
+        $floatBytes = "\xC3\xF5\x48\x40"; // IEEE 754 representation of 3.14
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -76,7 +76,7 @@ public function testReadFloatWithValidValue(): void
     public function testReadFloatWithZero(): void
     {
         // Test reading zero float
-        $floatBytes = pack('g', 0.0);
+        $floatBytes = "\x00\x00\x00\x00"; // IEEE 754 representation of 0.0
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -91,7 +91,7 @@ public function testReadFloatWithZero(): void
     public function testReadFloatWithNegativeValue(): void
     {
         // Test reading a negative float
-        $floatBytes = pack('g', -2.5);
+        $floatBytes = "\x00\x00\x20\xC0"; // IEEE 754 representation of -2.5
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -106,7 +106,7 @@ public function testReadFloatWithNegativeValue(): void
     public function testReadFloatWithInfinity(): void
     {
         // Test reading infinity
-        $floatBytes = pack('g', INF);
+        $floatBytes = "\x00\x00\x80\x7F"; // IEEE 754 representation of +infinity
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -121,7 +121,7 @@ public function testReadFloatWithInfinity(): void
     public function testReadFloatWithNaN(): void
     {
         // Test reading NaN
-        $floatBytes = pack('g', NAN);
+        $floatBytes = "\x00\x00\xC0\x7F"; // IEEE 754 representation of NaN
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -136,7 +136,7 @@ public function testReadFloatWithNaN(): void
     public function testReadDoubleWithValidValue(): void
     {
         // Test reading a double value (3.14159265359)
-        $doubleBytes = pack('e', 3.14159265359);
+        $doubleBytes = "\xEA\x2E\x44\x54\xFB\x21\x09\x40"; // IEEE 754 representation of 3.14159265359
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -151,7 +151,7 @@ public function testReadDoubleWithValidValue(): void
     public function testReadDoubleWithZero(): void
     {
         // Test reading zero double
-        $doubleBytes = pack('e', 0.0);
+        $doubleBytes = "\x00\x00\x00\x00\x00\x00\x00\x00"; // IEEE 754 representation of 0.0
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -166,7 +166,7 @@ public function testReadDoubleWithZero(): void
     public function testReadDoubleWithNegativeValue(): void
     {
         // Test reading a negative double
-        $doubleBytes = pack('e', -2.71828182846);
+        $doubleBytes = "\xCF\x5F\x14\x8B\x0A\xBF\x05\xC0"; // IEEE 754 representation of -2.71828182846
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -181,7 +181,7 @@ public function testReadDoubleWithNegativeValue(): void
     public function testReadDoubleWithInfinity(): void
     {
         // Test reading infinity
-        $doubleBytes = pack('e', INF);
+        $doubleBytes = "\x00\x00\x00\x00\x00\x00\xF0\x7F"; // IEEE 754 representation of +infinity
 
         $this->stream->expects($this->once())
             ->method('read')
@@ -196,7 +196,7 @@ public function testReadDoubleWithInfinity(): void
     public function testReadDoubleWithNaN(): void
     {
         // Test reading NaN
-        $doubleBytes = pack('e', NAN);
+        $doubleBytes = "\x00\x00\x00\x00\x00\x00\xF8\x7F"; // IEEE 754 representation of NaN
 
         $this->stream->expects($this->once())
             ->method('read')
diff --git a/tests/Unit/Serialization/BinaryEncoderTest.php b/tests/Unit/Serialization/BinaryEncoderTest.php
new file mode 100644
index 0000000..27a009f
--- /dev/null
+++ b/tests/Unit/Serialization/BinaryEncoderTest.php
@@ -0,0 +1,121 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Auxmoney\Avro\Tests\Unit\Serialization;
+
+use Auxmoney\Avro\Contracts\WritableStreamInterface;
+use Auxmoney\Avro\Serialization\BinaryEncoder;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+
+class BinaryEncoderTest extends TestCase
+{
+    private BinaryEncoder $encoder;
+    private WritableStreamInterface&\PHPUnit\Framework\MockObject\MockObject $stream;
+
+    protected function setUp(): void
+    {
+        $this->encoder = new BinaryEncoder();
+        $this->stream = $this->createMock(WritableStreamInterface::class);
+    }
+
+    #[DataProvider('encodeLongDataProvider')]
+    public function testWriteLong(int $value, string $expectedEncoding): void
+    {
+        $this->stream->expects($this->once())
+            ->method('write')
+            ->with($expectedEncoding);
+
+        $this->encoder->writeLong($this->stream, $value);
+    }
+
+    public function testWriteStringWithEmptyString(): void
+    {
+        $value = '';
+        $expectedLengthEncoding = "\x00"; // length 0 encoded as long
+
+        $this->stream->expects($this->once())
+            ->method('write')
+            ->with($expectedLengthEncoding);
+
+        $this->encoder->writeString($this->stream, $value);
+    }
+
+    public function testWriteStringWithNonEmptyString(): void
+    {
+        $value = 'Hello, World!';
+        $length = strlen($value);
+        $expectedLengthEncoding = "\x1A"; // length 13 encoded as long
+
+        $this->stream->expects($this->exactly(2))
+            ->method('write');
+
+        $this->encoder->writeString($this->stream, $value);
+    }
+
+    public function testEncodeFloat(): void
+    {
+        $value = 123.45;
+        $result = $this->encoder->encodeFloat($value);
+
+        // Verify it's a 4-byte float encoding
+        $this->assertSame(4, strlen($result));
+
+        // Verify the exact byte representation
+        $expectedBytes = "\x66\xE6\xF6\x42"; // IEEE 754 representation of 123.45
+        $this->assertSame($expectedBytes, $result);
+    }
+
+    public function testEncodeDouble(): void
+    {
+        $value = 123.456789;
+        $result = $this->encoder->encodeDouble($value);
+
+        // Verify it's an 8-byte double encoding
+        $this->assertSame(8, strlen($result));
+
+        // Verify the exact byte representation
+        $expectedBytes = "\x0B\x0B\xEE\x07\x3C\xDD\x5E\x40"; // IEEE 754 representation of 123.456789
+        $this->assertSame($expectedBytes, $result);
+    }
+
+    /**
+     * @return array<int, array{0: int, 1: string}>
+     */
+    public static function encodeLongDataProvider(): array
+    {
+        return [
+            // Negative values
+            [(int) -9223372036854775808, "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\x01"],
+            [-(1 << 62), "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\x7F"],
+            [-(1 << 61), "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\x3F"],
+            [-4294967295, "\xFD\xFF\xFF\xFF\x1F"],
+            [-(1 << 24), "\xFF\xFF\xFF\x0F"],
+            [-(1 << 16), "\xFF\xFF\x07"],
+            [-255, "\xFD\x03"],
+            [-128, "\xFF\x01"],
+            [-127, "\xFD\x01"],
+            [-10, "\x13"],
+            [-3, "\x05"],
+            [-2, "\x03"],
+            [-1, "\x01"],
+
+            // Zero and positive values
+            [0, "\x00"],
+            [1, "\x02"],
+            [2, "\x04"],
+            [3, "\x06"],
+            [10, "\x14"],
+            [127, "\xFE\x01"],
+            [128, "\x80\x02"],
+            [255, "\xFE\x03"],
+            [1 << 16, "\x80\x80\x08"],
+            [1 << 24, "\x80\x80\x80\x10"],
+            [4294967295, "\xFE\xFF\xFF\xFF\x1F"],
+            [1 << 61, "\x80\x80\x80\x80\x80\x80\x80\x80\x40"],
+            [1 << 62, "\x80\x80\x80\x80\x80\x80\x80\x80\x80\x01"],
+            [9223372036854775807, "\xFE\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\x01"],
+        ];
+    }
+}