Add test for unsupported subcommands

external-sop/src/test/java/sop/external/AbstractExternalSOPTest.java

@@ -141,7 +141,7 @@ public abstract class AbstractExternalSOPTest {
         }
     }
 
-    private static String readSopBackendFromProperties() {
+    static String readSopBackendFromProperties() {
         Properties properties = new Properties();
         try {
             InputStream resourceIn = AbstractExternalSOPTest.class.getResourceAsStream("backend.local.properties");

external-sop/src/test/java/sop/external/UnsupportedSubcommandTest.java

@@ -0,0 +1,58 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop.external;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledIf;
+import sop.exception.SOPGPException;
+
+import java.io.IOException;
+import java.util.Properties;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assumptions.assumeTrue;
+
+@EnabledIf("sop.external.AbstractExternalSOPTest#isExternalSopInstalled")
+public class UnsupportedSubcommandTest extends AbstractExternalSOPTest {
+
+    private final UnsupportedSubcommandExternal unsupportedSubcommand;
+
+    public UnsupportedSubcommandTest() {
+        String backend = readSopBackendFromProperties();
+        assumeTrue(backend != null);
+        Properties environment = readBackendEnvironment();
+        unsupportedSubcommand = new UnsupportedSubcommandExternal(backend, environment);
+    }
+
+    @Test
+    public void testUnsupportedSubcommand() {
+        // "sop unsupported" returns error code UNSUPPORTED_SUBCOMMAND
+        assertThrows(SOPGPException.UnsupportedSubcommand.class,
+                unsupportedSubcommand::executeUnsupportedSubcommand);
+    }
+
+    private static class UnsupportedSubcommandExternal {
+
+        private final Runtime runtime = Runtime.getRuntime();
+        private final String binary;
+        private final Properties environment;
+
+        public UnsupportedSubcommandExternal(String binaryName, Properties environment) {
+            this.binary = binaryName;
+            this.environment = environment;
+        }
+
+        public void executeUnsupportedSubcommand() {
+            String[] command = new String[] {binary, "unsupported"}; // ~$ sop unsupported
+            String[] env = ExternalSOP.propertiesToEnv(environment).toArray(new String[0]);
+            try {
+                Process process = runtime.exec(command, env);
+                ExternalSOP.finish(process);
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+}