WIP: add test for FileListPreprocessor

This test calls uiService.setHeadless(false) in order to set its custom default UI.

The test currently passes locally (because the last assertion - the issue I'd like to fix - is commented out), but does it on CI?

src/test/java/org/scijava/ui/FileListPreprocessorTest.java

@@ -0,0 +1,110 @@
+package org.scijava.ui;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import java.io.File;
+import java.io.FileFilter;
+import java.util.concurrent.ExecutionException;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.scijava.Context;
+import org.scijava.command.Command;
+import org.scijava.command.CommandInfo;
+import org.scijava.module.Module;
+import org.scijava.module.ModuleService;
+import org.scijava.plugin.Parameter;
+import org.scijava.ui.headless.HeadlessUI;
+
+public class FileListPreprocessorTest {
+
+	public static final String DUMMY_FILE_NAME = "dummy_file";
+	private Context context;
+	private ModuleService moduleService;
+
+	@Before
+	public void setUp() {
+		context = new Context();
+		context.service(UIService.class).setDefaultUI(new CustomUI());
+		context.service(UIService.class).setHeadless(false);
+		moduleService = context.service(ModuleService.class);
+	}
+
+	@After
+	public void tearDown() {
+		context.dispose();
+	}
+
+	@Test
+	public void test() throws InterruptedException, ExecutionException {
+		// assert that single File[] parameters get filled by ui.chooseFiles()
+		CommandInfo info = new CommandInfo(SingleParameterFileListCommand.class);
+		Module mod = moduleService.run(info, true).get();
+		assertNotNull(mod);
+		assertEquals(DUMMY_FILE_NAME, ((File[])mod.getInput("inputFiles"))[0].getName());
+
+		// assert that the presence of any other unresolved parameters prevents
+		// calls to ui.chooseFiles()
+		CommandInfo info2 = new CommandInfo(ParameterFileListAndOthersCommand.class);
+		Module mod2 = moduleService.run(info2, true).get();
+		assertNotNull(mod2);
+		assertNull(mod2.getInput("inputFiles"));
+
+		// assert that 'autoFill = false' prevents calls to ui.chooseFiles()
+		CommandInfo info3 = new CommandInfo(NoAutofillParameterFileListCommand.class);
+		Module mod3 = moduleService.run(info3, true).get();
+		assertNotNull(mod3);
+		// TODO this should not trigger ui.chooseFiles()
+		//assertNull(mod3.getInput("inputFiles"));
+	}
+
+	private class CustomUI extends HeadlessUI {
+
+		@Override
+		public File[] chooseFiles(File parent, File[] files, FileFilter filter, String style) {
+			return new File[] { new File(DUMMY_FILE_NAME) };
+		}
+	}
+
+	public static class SingleParameterFileListCommand implements Command {
+
+		@Parameter(persist = false)
+		private File[] inputFiles;
+
+		@Override
+		public void run() {
+			// do nothing
+		}
+
+	}
+
+	public static class ParameterFileListAndOthersCommand implements Command {
+
+		@Parameter(persist = false)
+		private File[] inputFiles;
+
+		@Parameter(required = false)
+		private String dummyString;
+
+		@Override
+		public void run() {
+			// do nothing
+		}
+
+	}
+
+	public static class NoAutofillParameterFileListCommand implements Command {
+
+		@Parameter(autoFill = false, persist = false)
+		private File[] inputFiles;
+
+		@Override
+		public void run() {
+			// do nothing
+		}
+
+	}
+}