diff --git a/sop-java-picocli/src/test/java/sop/cli/picocli/commands/AbstractSopCmdTest.java b/sop-java-picocli/src/test/java/sop/cli/picocli/commands/AbstractSopCmdTest.java
new file mode 100644
index 0000000..7038ad7
--- /dev/null
+++ b/sop-java-picocli/src/test/java/sop/cli/picocli/commands/AbstractSopCmdTest.java
@@ -0,0 +1,126 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop.cli.picocli.commands;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.opentest4j.TestAbortedException;
+import sop.cli.picocli.TestFileUtil;
+import sop.exception.SOPGPException;
+
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class AbstractSopCmdTest {
+
+    private static AbstractSopCmd abstractCmd;
+    private static final TestEnvironmentVariableResolver resolver = new TestEnvironmentVariableResolver();
+
+    @BeforeAll
+    public static void setup() {
+        abstractCmd = new VersionCmd(); // Use Version as representative command
+        abstractCmd.setEnvironmentVariableResolver(resolver);
+    }
+
+    @Test
+    public void setEnvironmentVariableResolver_nullNPE() {
+        assertThrows(NullPointerException.class, () -> abstractCmd.setEnvironmentVariableResolver(null));
+    }
+
+    @Test
+    public void getInput_NullInvalid() {
+        assertThrows(IllegalArgumentException.class, () -> abstractCmd.getInput(null));
+    }
+
+    @Test
+    public void getInput_EmptyInvalid() {
+        assertThrows(IllegalArgumentException.class, () -> abstractCmd.getInput(""));
+    }
+
+    @Test
+    public void getInput_BlankInvalid() {
+        assertThrows(IllegalArgumentException.class, () -> abstractCmd.getInput("    "));
+    }
+
+    @Test
+    public void getInput_envNotSetIllegalArg() {
+        String envName = "@ENV:IS_NOT_SET";
+        assertThrows(IllegalArgumentException.class, () -> abstractCmd.getInput(envName));
+    }
+
+    @Test
+    public void getInput_envEmptyIllegalArg() {
+        String envName = "@ENV:IS_EMPTY";
+        resolver.addEnvironmentVariable("IS_EMPTY", "");
+        assertThrows(IllegalArgumentException.class, () -> abstractCmd.getInput(envName));
+    }
+
+    @Test
+    public void getInput_fromEnv() throws IOException {
+        resolver.addEnvironmentVariable("FOO", "BAR");
+        InputStream input = abstractCmd.getInput("@ENV:FOO");
+        String string = readStringFromInputStream(input);
+        assertEquals("BAR", string);
+    }
+
+    private static String readStringFromInputStream(InputStream input)
+            throws IOException {
+        ByteArrayOutputStream output = new ByteArrayOutputStream();
+
+        byte[] buf = new byte[512];
+        int read;
+        while ((read = input.read(buf)) > 0) {
+            output.write(buf, 0, read);
+        }
+        return output.toString();
+    }
+
+    @Test
+    public void getInput_envClashesWithExistingFile() throws IOException {
+        String env = "@ENV:existing.file";
+        File tempFile = new File(env);
+        if (!tempFile.createNewFile()) {
+            throw new TestAbortedException("Cannot create temporary file " + tempFile.getAbsolutePath());
+        }
+        tempFile.deleteOnExit();
+
+        resolver.addEnvironmentVariable("existing.file", "foo_bar");
+
+        assertThrows(SOPGPException.AmbiguousInput.class, () -> abstractCmd.getInput(env));
+    }
+
+    @Test
+    public void getInput_fdClashesWithExistingFile() throws IOException {
+        String env = "@FD:existing.file";
+        File tempFile = new File(env);
+        if (!tempFile.createNewFile()) {
+            throw new TestAbortedException("Cannot create temporary file " + tempFile.getAbsolutePath());
+        }
+        tempFile.deleteOnExit();
+
+        resolver.addEnvironmentVariable("existing.file", "foo_bar");
+
+        assertThrows(SOPGPException.AmbiguousInput.class, () -> abstractCmd.getInput(env));
+    }
+
+    @Test
+    public void getInput_missingFile() {
+        String missingFile = "missing.file";
+        assertThrows(SOPGPException.MissingInput.class, () -> abstractCmd.getInput(missingFile));
+    }
+
+    @Test
+    public void getInput_notAFile() throws IOException {
+        File directory = TestFileUtil.createTempDir();
+        directory.deleteOnExit();
+
+        assertThrows(SOPGPException.MissingInput.class, () -> abstractCmd.getInput(directory.getAbsolutePath()));
+    }
+}
diff --git a/sop-java-picocli/src/test/java/sop/cli/picocli/commands/TestEnvironmentVariableResolver.java b/sop-java-picocli/src/test/java/sop/cli/picocli/commands/TestEnvironmentVariableResolver.java
new file mode 100644
index 0000000..6665ada
--- /dev/null
+++ b/sop-java-picocli/src/test/java/sop/cli/picocli/commands/TestEnvironmentVariableResolver.java
@@ -0,0 +1,22 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop.cli.picocli.commands;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class TestEnvironmentVariableResolver implements AbstractSopCmd.EnvironmentVariableResolver {
+
+    private final Map<String, String> environment = new HashMap<>();
+
+    public void addEnvironmentVariable(String name, String value) {
+        this.environment.put(name, value);
+    }
+
+    @Override
+    public String resolveEnvironmentVariable(String name) {
+        return environment.get(name);
+    }
+}