Unit tests for APK version parsing & fix typo in parser

Package.swift

@@ -12,14 +12,21 @@ let package = Package(
   targets: [
     .target(
       name: "darwin-apk",
-      path: "Sources/apk"),
+      path: "Sources/apk",
+    ),
+    .testTarget(
+      name: "darwin-apk-tests",
+      dependencies: [
+        "darwin-apk",
+      ],
+    ),
     .executableTarget(
       name: "dpk",
       dependencies: [
         "darwin-apk",
         .product(name: "ArgumentParser", package: "swift-argument-parser"),
       ],
-      path: "Sources/dpk-cli"
+      path: "Sources/dpk-cli",
     ),
-  ]
+  ],
 )

Sources/apk/Version/ApkVersionReader.swift

@@ -16,7 +16,7 @@ internal struct ApkVersionReader {
   mutating func next() throws(Invalid) -> TokenPart {
     self.seen.formUnion(self.last)
 
-    switch string.first ?? UInt8(ascii: "0") {
+    switch string.first ?? UInt8(ascii: "\0") {
     case UInt8(ascii: "a")...UInt8(ascii: "z"):  // Letter suffix
       guard self.seen.contains(.initial),
           self.last.isDisjoint(with: [ .letter, .suffix, .suffixNumber, .commitHash, .revision ]) else {

Tests/darwin-apk-tests/ApkVersionTests.swift

@@ -0,0 +1,47 @@
+/*
+ * darwin-apk © 2025 Gay Pizza Specifications
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import Testing
+@testable import darwin_apk
+
+@Test func testParseDependency() {
+  for valid in [
+    "bash",
+    "libapparmor=4.1.0-r2",
+    "python3~3.12",
+    "so:libc.musl-x86_64.so.1",
+    "!alsa-lib<1.2.14-r0",
+    "!alsa-lib>1.2.14-r0",
+    "!lld20-libs<20.1.2-r0",
+    "!lld20-libs>20.1.2-r0",
+    "!lld20<20.1.2-r0",
+    "!lld20>20.1.2-r0",
+  ] {
+    #expect(throws: Never.self, "Expected valid: \(valid)") {
+      try ApkVersionRequirement(extract: valid[...])
+    }
+  }
+}
+
+@Test func testVersionValidation() {
+  for valid in [
+    "100",
+    "1.0",
+    "0-r1",
+    "10.2.3-r100",
+    "0.0.0_git20210122-r0",
+    "0.20240527.191746-r2",
+    "9100h-r4",
+  ] {
+    #expect(ApkVersionCompare.validate(valid), "Should be valid: \(valid)")
+  }
+  for invalid in [
+    "a",
+    "0r-10",
+    "10.2.3-100",
+  ] {
+    #expect(!ApkVersionCompare.validate(invalid), "Should be invalid: \(invalid)")
+  }
+}