Give mixed selections something to do

A Drag of different kinds showed an empty wheel, because the catalog only
answers for a single category. Filee's answer is a mixed profile, so add
Zip (one archive, flat names) and Merge (non-PDFs are converted to PDF
first); a multi-file drag of one kind gets Zip too.

Sources/Konverter/SelfTest.swift

@@ -1,6 +1,7 @@
 import AppKit
 import CoreGraphics
 import Foundation
+import PDFKit
 
 /// `--self-test` exercises the real conversion paths end to end and exits
 /// non-zero on failure. Kept in the shipped binary so a build can be verified
@@ -29,6 +30,7 @@ enum SelfTest {
         testDocuments()
         testAudio()
         testEbook()
+        testCombining()
         testGeometry()
 
         print("")
@@ -224,6 +226,25 @@ enum SelfTest {
             try ArchiveConverter.convert(source: folder, to: .tar, at: tar)
             try requireFile(tar)
         }
+
+        check("several files → one zip") {
+            let first = directory.appendingPathComponent("note.txt")
+            let second = directory.appendingPathComponent("spreadsheet.csv")
+            try? "one".write(to: first, atomically: true, encoding: .utf8)
+            try? "a,b\n1,2\n".write(to: second, atomically: true, encoding: .utf8)
+            let zip = directory.appendingPathComponent("selection.zip")
+            try ArchiveConverter.createArchive(from: [first, second], at: zip)
+            try requireFile(zip)
+
+            let target = directory.appendingPathComponent("selection-unpacked", isDirectory: true)
+            try ArchiveConverter.extract(source: zip, into: target)
+            for name in ["note.txt", "spreadsheet.csv"] {
+                let entry = target.appendingPathComponent(name)
+                guard FileManager.default.fileExists(atPath: entry.path) else {
+                    throw TestFailure("\(name) missing from the archive")
+                }
+            }
+        }
     }
 
     private static func testDocuments() {
@@ -325,6 +346,59 @@ enum SelfTest {
         }
     }
 
+    /// Filee's "mixed profile": a drag of different kinds still has something
+    /// useful to do, instead of an empty wheel.
+    private static func testCombining() {
+        section("Mixed selections")
+        let photo = directory.appendingPathComponent("sample.png")
+        let pdf = directory.appendingPathComponent("sample.pdf")
+        let note = directory.appendingPathComponent("note.txt")
+
+        check("a mixed drag still gets a wheel") {
+            let items = WheelBuilder.items(kind: .convert, urls: [photo, pdf])
+            let tools = items.compactMap { item -> ToolID? in
+                if case .tool(let tool) = item.payload { return tool }
+                return nil
+            }
+            guard !items.isEmpty else { throw TestFailure("the convert wheel was empty") }
+            guard tools.contains(.mergePDF), tools.contains(.createArchive) else {
+                throw TestFailure("expected Merge and Zip, got \(tools.map(\.rawValue))")
+            }
+        }
+
+        check("a multi-file wheel can always be zipped") {
+            let items = WheelBuilder.items(kind: .tools, urls: [photo, directory.appendingPathComponent("note.txt")])
+            let tools = items.compactMap { item -> ToolID? in
+                if case .tool(let tool) = item.payload { return tool }
+                return nil
+            }
+            guard tools.contains(.createArchive) else {
+                throw TestFailure("Zip is missing from a two-file image wheel")
+            }
+        }
+
+        check("photos and pdfs merge into one pdf") {
+            let outcome = try ToolRunner.run(tool: .mergePDF, inputs: [photo, pdf], params: ToolParams())
+            guard let merged = outcome.outputs.first,
+                  let document = PDFDocument(url: merged) else {
+                throw TestFailure("no merged pdf was produced")
+            }
+            guard document.pageCount >= 2 else {
+                throw TestFailure("merged pdf has \(document.pageCount) page(s)")
+            }
+        }
+
+        check("any files → one zip") {
+            let outcome = try ToolRunner.run(tool: .createArchive, inputs: [note, photo], params: ToolParams())
+            guard let zip = outcome.outputs.first else { throw TestFailure("no archive was produced") }
+            try requireFile(zip)
+            let entries = try ArchiveConverter.list(zip)
+            for name in ["note.txt", "sample.png"] where !entries.contains(name) {
+                throw TestFailure("\(name) is missing from the archive: \(entries)")
+            }
+        }
+    }
+
     private static func testGeometry() {
         section("Wheel geometry")
         let frame = CGRect(x: 0, y: 0, width: 400, height: 400)