diff --git a/EAN13View/Source/EAN13BarcodeGenerator.swift b/EAN13View/Source/EAN13BarcodeGenerator.swift
index 47d5fc9..ba93b16 100644
--- a/EAN13View/Source/EAN13BarcodeGenerator.swift
+++ b/EAN13View/Source/EAN13BarcodeGenerator.swift
@@ -1,18 +1,18 @@
 struct EAN13BarcodeGenerator{
     
-    struct DigitEndcoding {
+    struct DigitEncoding {
         
-        enum EndCoding: String {
+        enum Encoding: String {
             case l
             case g
             case r
         }
         
         let bitValue: String
-        init?(value: Int, endCoding: EndCoding) {
+        init?(value: Int, encoding: Encoding) {
             guard value <= 9 && value >= 0 else { return nil }
-            let code = DigitEndcoding.rValues[value]
-            switch endCoding {
+            let code = DigitEncoding.rValues[value]
+            switch encoding {
             case .r:
                 bitValue = String(code, radix: 2)
             case .g:
@@ -50,15 +50,16 @@ struct EAN13BarcodeGenerator{
     ]
     
     func generate(value: [Int]) -> [Bool]{
-        let secondEndcoding = secondCoding[value.first!]
-            .toEndCoding()
+        guard let firstDigit = value.first else { return [] }
+        let secondEncoding = secondCoding[firstDigit]
+            .toEncoding()
         let second = zip(value[1...6], 0...5).compactMap{ value, index -> String in
-            return DigitEndcoding(value: value, endCoding: secondEndcoding[index])!.bitValue
+            return DigitEncoding(value: value, encoding: secondEncoding[index])?.bitValue ?? ""
             }.reduce("", { a, b in
                 a + b
             })
         let third = value[7...12].compactMap{ value -> String in
-            return DigitEndcoding(value: value, endCoding: .r)!.bitValue
+            return DigitEncoding(value: value, encoding: .r)?.bitValue ?? ""
             }.reduce("", { a, b in
                 a + b
             })
diff --git a/EAN13View/Source/EAN13Validator.swift b/EAN13View/Source/EAN13Validator.swift
index 91a3cb8..87196e6 100644
--- a/EAN13View/Source/EAN13Validator.swift
+++ b/EAN13View/Source/EAN13Validator.swift
@@ -3,13 +3,18 @@ struct EAN13Validator{
     func isValid(value: [Int]) -> Bool{
         guard value.count == 13 else { return false }
         
-        let even = value.prefix(12).filter{$0 % 2 == 0}.reduce(0) { a, b in
-            a + b
-        }
-        let odd = value.prefix(12).filter{$0 % 2 == 1}.reduce(0) { a, b in
-            a + b
+        var sumOddPosition = 0
+        var sumEvenPosition = 0
+        
+        for (index, digit) in value.prefix(12).enumerated() {
+            if index % 2 == 0 {
+                sumOddPosition += digit
+            } else {
+                sumEvenPosition += digit
+            }
         }
-        let checkDigit = (10 - (even + odd * 3) % 10) % 10
-        return value.last! == checkDigit
+        
+        let checkDigit = (10 - (sumOddPosition + sumEvenPosition * 3) % 10) % 10
+        return value.last == checkDigit
     }
 }
diff --git a/EAN13View/Source/String+EAN13.swift b/EAN13View/Source/String+EAN13.swift
index fae20e7..472471a 100644
--- a/EAN13View/Source/String+EAN13.swift
+++ b/EAN13View/Source/String+EAN13.swift
@@ -1,9 +1,9 @@
 extension String{
-    func toEndCoding() -> [EAN13BarcodeGenerator.DigitEndcoding.EndCoding]{
+    func toEncoding() -> [EAN13BarcodeGenerator.DigitEncoding.Encoding]{
         return self.lowercased().compactMap {
             EAN13BarcodeGenerator
-                .DigitEndcoding
-                .EndCoding(rawValue: String($0))
+                .DigitEncoding
+                .Encoding(rawValue: String($0))
         }
     }
 }
diff --git a/Package.swift b/Package.swift
index d7bdfbc..7177b07 100644
--- a/Package.swift
+++ b/Package.swift
@@ -19,5 +19,9 @@ let package = Package(
             path: "EAN13View/Source",
             publicHeadersPath: ".."
         ),
+        .testTarget(
+            name: "EAN13ViewTests",
+            dependencies: ["EAN13View"]
+        ),
     ]
 )
diff --git a/Tests/EAN13ViewTests/EAN13ViewTests.swift b/Tests/EAN13ViewTests/EAN13ViewTests.swift
new file mode 100644
index 0000000..b4228fe
--- /dev/null
+++ b/Tests/EAN13ViewTests/EAN13ViewTests.swift
@@ -0,0 +1,56 @@
+import XCTest
+@testable import EAN13View
+
+final class EAN13ViewTests: XCTestCase {
+    
+    func testValidatorValidEAN() {
+        // Known valid EAN
+        let validEAN = "5901234123457"
+        XCTAssertNoThrow(try EAN13(value: validEAN))
+    }
+    
+    func testValidatorInvalidEAN_WrongCheckDigit() {
+        // Last digit changed from 7 to 8
+        let invalidEAN = "5901234123458"
+        XCTAssertThrowsError(try EAN13(value: invalidEAN)) { error in
+            XCTAssertEqual(error as? EAN13.Error, EAN13.Error.invalidEAN)
+        }
+    }
+    
+    func testValidatorInvalidEAN_SwappedDigits() {
+        // Swapped first two digits: 9501234123457
+        // Previous buggy validator would accept this.
+        let invalidEAN = "9501234123457"
+        XCTAssertThrowsError(try EAN13(value: invalidEAN)) { error in
+            XCTAssertEqual(error as? EAN13.Error, EAN13.Error.invalidEAN)
+        }
+    }
+    
+    func testGeneratorStructure() {
+        let validEAN = "5901234123457"
+        guard let ean = try? EAN13(value: validEAN) else {
+            XCTFail("Should be valid EAN")
+            return
+        }
+        
+        // EAN13 total modules should be 95
+        XCTAssertEqual(ean.lines.count, 95)
+        
+        // Start marker 101
+        XCTAssertEqual(ean.lines[0], true)
+        XCTAssertEqual(ean.lines[1], false)
+        XCTAssertEqual(ean.lines[2], true)
+        
+        // End marker 101
+        XCTAssertEqual(ean.lines[92], true)
+        XCTAssertEqual(ean.lines[93], false)
+        XCTAssertEqual(ean.lines[94], true)
+    }
+
+    static var allTests = [
+        ("testValidatorValidEAN", testValidatorValidEAN),
+        ("testValidatorInvalidEAN_WrongCheckDigit", testValidatorInvalidEAN_WrongCheckDigit),
+        ("testValidatorInvalidEAN_SwappedDigits", testValidatorInvalidEAN_SwappedDigits),
+        ("testGeneratorStructure", testGeneratorStructure),
+    ]
+}
diff --git a/Tests/EAN13ViewTests/XCTestManifests.swift b/Tests/EAN13ViewTests/XCTestManifests.swift
new file mode 100644
index 0000000..3e2b9ab
--- /dev/null
+++ b/Tests/EAN13ViewTests/XCTestManifests.swift
@@ -0,0 +1,9 @@
+import XCTest
+
+#if !canImport(ObjectiveC)
+public func allTests() -> [XCTestCaseEntry] {
+    return [
+        testCase(EAN13ViewTests.allTests),
+    ]
+}
+#endif
diff --git a/Tests/LinuxMain.swift b/Tests/LinuxMain.swift
new file mode 100644
index 0000000..a20020b
--- /dev/null
+++ b/Tests/LinuxMain.swift
@@ -0,0 +1,7 @@
+import XCTest
+
+import EAN13ViewTests
+
+var tests = [XCTestCaseEntry]()
+tests += EAN13ViewTests.allTests()
+XCTMain(tests)