diff --git a/Tests/LinuxMain.swift b/Tests/LinuxMain.swift
index 8f37320..6204cc4 100644
--- a/Tests/LinuxMain.swift
+++ b/Tests/LinuxMain.swift
@@ -4,4 +4,10 @@ import NullCodableTests
 
 var tests = [XCTestCaseEntry]()
 tests += NullCodableTests.allTests()
+tests += NullCodablePropertyWrapperTests.allTests()
+tests += NullCodableJSONEncoderTests.allTests()
+tests += NullCodableJSONDecoderTests.allTests()
+tests += NullCodableComplexStructTests.allTests()
+tests += NullCodableEquatableTests.allTests()
+tests += NullCodableSendableTests.allTests()
 XCTMain(tests)
diff --git a/Tests/NullCodableTests/NullCodableComplexStructTests.swift b/Tests/NullCodableTests/NullCodableComplexStructTests.swift
new file mode 100644
index 0000000..fe5afa9
--- /dev/null
+++ b/Tests/NullCodableTests/NullCodableComplexStructTests.swift
@@ -0,0 +1,119 @@
+import Foundation
+import XCTest
+@testable import NullCodable
+
+final class NullCodableComplexStructTests: XCTestCase {
+
+    private struct Address: Codable, Equatable {
+        let street: String
+        let city: String
+        let country: String
+    }
+
+    private struct LineItem: Codable, Equatable {
+        let name: String
+        let quantity: Int
+        let price: Decimal
+    }
+
+    private struct Customer: Codable, Equatable {
+        let name: String
+        @NullCodable var email: String?
+        let address: Address
+    }
+
+    private struct Order: Codable, Equatable {
+        let id: String
+        let customer: Customer
+        let items: [LineItem]
+        @NullCodable var notes: [String]?
+        @NullCodable var discount: Decimal?
+    }
+
+    func test_encodesComplexStructToJSON() throws {
+        let order = Order(
+            id: "order-123",
+            customer: Customer(
+                name: "Ada Lovelace",
+                email: nil,
+                address: Address(
+                    street: "1 Analytical Engine Way",
+                    city: "London",
+                    country: "United Kingdom"
+                )
+            ),
+            items: [
+                LineItem(name: "Notebook", quantity: 2, price: 12.50),
+                LineItem(name: "Pen", quantity: 1, price: 3.25),
+            ],
+            notes: nil,
+            discount: 5
+        )
+
+        let data = try JSONEncoder().encode(order)
+        let actual = try XCTUnwrap(JSONSerialization.jsonObject(with: data) as? NSDictionary)
+        let expected = try XCTUnwrap(JSONSerialization.jsonObject(with: Data("""
+        {
+          "id": "order-123",
+          "customer": {
+            "name": "Ada Lovelace",
+            "email": null,
+            "address": {
+              "street": "1 Analytical Engine Way",
+              "city": "London",
+              "country": "United Kingdom"
+            }
+          },
+          "items": [
+            { "name": "Notebook", "quantity": 2, "price": 12.5 },
+            { "name": "Pen", "quantity": 1, "price": 3.25 }
+          ],
+          "notes": null,
+          "discount": 5
+        }
+        """.utf8)) as? NSDictionary)
+
+        XCTAssertTrue(actual.isEqual(expected))
+    }
+
+    func test_decodesComplexStructFromJSON() throws {
+        let json = """
+        {
+          "id": "order-123",
+          "customer": {
+            "name": "Ada Lovelace",
+            "email": "ada@example.com",
+            "address": {
+              "street": "1 Analytical Engine Way",
+              "city": "London",
+              "country": "United Kingdom"
+            }
+          },
+          "items": [
+            { "name": "Notebook", "quantity": 2, "price": 12.5 },
+            { "name": "Pen", "quantity": 1, "price": 3.25 }
+          ],
+          "notes": ["Gift wrap"],
+          "discount": null
+        }
+        """
+
+        let order = try JSONDecoder().decode(Order.self, from: Data(json.utf8))
+
+        XCTAssertEqual(order.id, "order-123")
+        XCTAssertEqual(order.customer.name, "Ada Lovelace")
+        XCTAssertEqual(order.customer.email, "ada@example.com")
+        XCTAssertEqual(order.customer.address.city, "London")
+        XCTAssertEqual(order.items, [
+            LineItem(name: "Notebook", quantity: 2, price: 12.5),
+            LineItem(name: "Pen", quantity: 1, price: 3.25),
+        ])
+        XCTAssertEqual(order.notes, ["Gift wrap"])
+        XCTAssertNil(order.discount)
+    }
+
+    static let allTests = [
+        ("test_encodesComplexStructToJSON", test_encodesComplexStructToJSON),
+        ("test_decodesComplexStructFromJSON", test_decodesComplexStructFromJSON),
+    ]
+}
diff --git a/Tests/NullCodableTests/NullCodableEquatableTests.swift b/Tests/NullCodableTests/NullCodableEquatableTests.swift
new file mode 100644
index 0000000..bbf60eb
--- /dev/null
+++ b/Tests/NullCodableTests/NullCodableEquatableTests.swift
@@ -0,0 +1,28 @@
+import XCTest
+@testable import NullCodable
+
+final class NullCodableEquatableTests: XCTestCase {
+
+    func test_comparesWrappedValues() {
+        XCTAssertEqual(
+            NullCodable(wrappedValue: "value"),
+            NullCodable(wrappedValue: "value")
+        )
+        XCTAssertEqual(
+            NullCodable<String>(wrappedValue: nil),
+            NullCodable<String>(wrappedValue: nil)
+        )
+        XCTAssertNotEqual(
+            NullCodable(wrappedValue: "first"),
+            NullCodable(wrappedValue: "second")
+        )
+        XCTAssertNotEqual(
+            NullCodable<String>(wrappedValue: nil),
+            NullCodable(wrappedValue: "value")
+        )
+    }
+
+    static let allTests = [
+        ("test_comparesWrappedValues", test_comparesWrappedValues),
+    ]
+}
diff --git a/Tests/NullCodableTests/NullCodableJSONDecoderTests.swift b/Tests/NullCodableTests/NullCodableJSONDecoderTests.swift
new file mode 100644
index 0000000..50a9fa8
--- /dev/null
+++ b/Tests/NullCodableTests/NullCodableJSONDecoderTests.swift
@@ -0,0 +1,53 @@
+import XCTest
+@testable import NullCodable
+
+final class NullCodableJSONDecoderTests: XCTestCase {
+
+    func test_decodesJSONNullAsNil() throws {
+        let value = try JSONDecoder().decode(
+            NullCodable<String>.self,
+            from: Data("null".utf8)
+        )
+
+        XCTAssertNil(value.wrappedValue)
+    }
+
+    func test_decodesWrappedValue() throws {
+        let value = try JSONDecoder().decode(
+            NullCodable<Int>.self,
+            from: Data("42".utf8)
+        )
+
+        XCTAssertEqual(value.wrappedValue, 42)
+    }
+
+    func test_decodesInvalidWrappedValueWithAnError() {
+        XCTAssertThrowsError(
+            try JSONDecoder().decode(
+                NullCodable<Int>.self,
+                from: Data("\"not an integer\"".utf8)
+            )
+        ) { error in
+            XCTAssertTrue(error is DecodingError)
+        }
+    }
+
+    func test_supportsCollectionValues() throws {
+        let value = NullCodable(wrappedValue: ["one", "two"])
+
+        let data = try JSONEncoder().encode(value)
+        let decoded = try JSONDecoder().decode(
+            NullCodable<[String]>.self,
+            from: data
+        )
+
+        XCTAssertEqual(decoded.wrappedValue, ["one", "two"])
+    }
+
+    static let allTests = [
+        ("test_decodesJSONNullAsNil", test_decodesJSONNullAsNil),
+        ("test_decodesWrappedValue", test_decodesWrappedValue),
+        ("test_decodesInvalidWrappedValueWithAnError", test_decodesInvalidWrappedValueWithAnError),
+        ("test_supportsCollectionValues", test_supportsCollectionValues),
+    ]
+}
diff --git a/Tests/NullCodableTests/NullCodableJSONEncoderTests.swift b/Tests/NullCodableTests/NullCodableJSONEncoderTests.swift
new file mode 100644
index 0000000..02a4d72
--- /dev/null
+++ b/Tests/NullCodableTests/NullCodableJSONEncoderTests.swift
@@ -0,0 +1,26 @@
+import XCTest
+@testable import NullCodable
+
+final class NullCodableJSONEncoderTests: XCTestCase {
+
+    func test_encodesNilAsJSONNull() throws {
+        let value = NullCodable<String>(wrappedValue: nil)
+
+        let data = try JSONEncoder().encode(value)
+
+        XCTAssertEqual(String(decoding: data, as: UTF8.self), "null")
+    }
+
+    func test_encodesWrappedValue() throws {
+        let value = NullCodable(wrappedValue: 42)
+
+        let data = try JSONEncoder().encode(value)
+
+        XCTAssertEqual(String(decoding: data, as: UTF8.self), "42")
+    }
+
+    static let allTests = [
+        ("test_encodesNilAsJSONNull", test_encodesNilAsJSONNull),
+        ("test_encodesWrappedValue", test_encodesWrappedValue),
+    ]
+}
diff --git a/Tests/NullCodableTests/NullCodablePropertyWrapperTests.swift b/Tests/NullCodableTests/NullCodablePropertyWrapperTests.swift
new file mode 100644
index 0000000..fdea90d
--- /dev/null
+++ b/Tests/NullCodableTests/NullCodablePropertyWrapperTests.swift
@@ -0,0 +1,26 @@
+import XCTest
+@testable import NullCodable
+
+final class NullCodablePropertyWrapperTests: XCTestCase {
+
+    func test_defaultValueIsNil() {
+        let value = NullCodable<String>(wrappedValue: nil)
+
+        XCTAssertNil(value.wrappedValue)
+    }
+
+    func test_wrappedValueCanBeReadAndUpdated() {
+        var value = NullCodable(wrappedValue: "before")
+
+        XCTAssertEqual(value.wrappedValue, "before")
+
+        value.wrappedValue = "after"
+
+        XCTAssertEqual(value.wrappedValue, "after")
+    }
+
+    static let allTests = [
+        ("test_defaultValueIsNil", test_defaultValueIsNil),
+        ("test_wrappedValueCanBeReadAndUpdated", test_wrappedValueCanBeReadAndUpdated),
+    ]
+}
diff --git a/Tests/NullCodableTests/NullCodableSendableTests.swift b/Tests/NullCodableTests/NullCodableSendableTests.swift
new file mode 100644
index 0000000..fc6f1ca
--- /dev/null
+++ b/Tests/NullCodableTests/NullCodableSendableTests.swift
@@ -0,0 +1,18 @@
+import XCTest
+@testable import NullCodable
+
+final class NullCodableSendableTests: XCTestCase {
+
+    func test_conformsToSendableWhenWrappedValueIsSendable() {
+        assertSendable(NullCodable(wrappedValue: "value"))
+        assertSendable(NullCodable(wrappedValue: 42))
+    }
+
+    private func assertSendable<T: Sendable>(_ value: T) {
+        _ = value
+    }
+
+    static let allTests = [
+        ("test_conformsToSendableWhenWrappedValueIsSendable", test_conformsToSendableWhenWrappedValueIsSendable),
+    ]
+}
diff --git a/Tests/NullCodableTests/NullCodableTests.swift b/Tests/NullCodableTests/NullCodableTests.swift
index 48845a7..6a6028b 100644
--- a/Tests/NullCodableTests/NullCodableTests.swift
+++ b/Tests/NullCodableTests/NullCodableTests.swift
@@ -129,7 +129,7 @@ final class NullCodableTests: XCTestCase {
         XCTAssertEqual(test.b, 42)
     }
     
-    static var allTests = [
+    static let allTests = [
         ("test_noConformance", test_noConformance),
         ("test_encodable", test_encodable),
         ("test_decodable", test_decodable),
diff --git a/Tests/NullCodableTests/XCTestManifests.swift b/Tests/NullCodableTests/XCTestManifests.swift
index c12daa2..5215fed 100644
--- a/Tests/NullCodableTests/XCTestManifests.swift
+++ b/Tests/NullCodableTests/XCTestManifests.swift
@@ -4,6 +4,12 @@ import XCTest
 public func allTests() -> [XCTestCaseEntry] {
     return [
         testCase(NullCodableTests.allTests),
+        testCase(NullCodablePropertyWrapperTests.allTests),
+        testCase(NullCodableJSONEncoderTests.allTests),
+        testCase(NullCodableJSONDecoderTests.allTests),
+        testCase(NullCodableComplexStructTests.allTests),
+        testCase(NullCodableEquatableTests.allTests),
+        testCase(NullCodableSendableTests.allTests),
     ]
 }
 #endif