diff --git a/external-sop/build.gradle b/external-sop/build.gradle
index 0f5055b..37bd8f3 100644
--- a/external-sop/build.gradle
+++ b/external-sop/build.gradle
@@ -16,6 +16,7 @@ dependencies {
     testImplementation "org.junit.jupiter:junit-jupiter-api:$junitVersion"
     testImplementation "org.junit.jupiter:junit-jupiter-params:$junitVersion"
     testRuntimeOnly "org.junit.jupiter:junit-jupiter-engine:$junitVersion"
+    // Read json config file
     testImplementation "com.google.code.gson:gson:2.10.1"
 
     api project(":sop-java")
@@ -23,9 +24,6 @@ dependencies {
     api "org.slf4j:slf4j-api:$slf4jVersion"
     testImplementation "ch.qos.logback:logback-classic:$logbackVersion"
 
-    // Compare version strings
-    implementation 'org.apache.maven:maven-artifact:3.6.3'
-    
     // @Nonnull, @Nullable...
     implementation "com.google.code.findbugs:jsr305:$jsrVersion"
 }
diff --git a/external-sop/src/test/java/sop/external/AbstractExternalSOPTest.java b/external-sop/src/test/java/sop/external/AbstractExternalSOPTest.java
index 3661d2a..824990f 100644
--- a/external-sop/src/test/java/sop/external/AbstractExternalSOPTest.java
+++ b/external-sop/src/test/java/sop/external/AbstractExternalSOPTest.java
@@ -17,32 +17,28 @@ import java.util.List;
 import java.util.Properties;
 import java.util.stream.Stream;
 
-import static org.junit.jupiter.api.Assumptions.assumeFalse;
-import static org.junit.jupiter.api.Assumptions.assumeTrue;
-
 public abstract class AbstractExternalSOPTest {
 
     private static final List<Arguments> backends = new ArrayList<>();
 
     static {
         TestSuite suite = readConfiguration();
-        assumeTrue(suite != null);
-        assumeFalse(suite.backends.isEmpty());
-
-        for (TestSubject subject : suite.backends) {
-            if (!new File(subject.sop).exists()) {
-                continue;
-            }
-
-            Properties env = new Properties();
-            if (subject.env != null) {
-                for (Var var : subject.env) {
-                    env.put(var.key, var.value);
+        if (suite != null && !suite.backends.isEmpty()) {
+            for (TestSubject subject : suite.backends) {
+                if (!new File(subject.sop).exists()) {
+                    continue;
                 }
-            }
 
-            SOP sop = new ExternalSOP(subject.sop, env);
-            backends.add(Arguments.of(Named.of(subject.name, sop)));
+                Properties env = new Properties();
+                if (subject.env != null) {
+                    for (Var var : subject.env) {
+                        env.put(var.key, var.value);
+                    }
+                }
+
+                SOP sop = new ExternalSOP(subject.sop, env);
+                backends.add(Arguments.of(Named.of(subject.name, sop)));
+            }
         }
     }
 
@@ -62,6 +58,10 @@ public abstract class AbstractExternalSOPTest {
         return suite;
     }
 
+    public static boolean hasBackends() {
+        return !backends.isEmpty();
+    }
+
     // JSON DTOs
 
     public static class TestSuite {
diff --git a/external-sop/src/test/java/sop/external/ExternalArmorDearmorRoundTripTest.java b/external-sop/src/test/java/sop/external/ExternalArmorDearmorRoundTripTest.java
index d6e4402..dec48f4 100644
--- a/external-sop/src/test/java/sop/external/ExternalArmorDearmorRoundTripTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalArmorDearmorRoundTripTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.SOP;
@@ -17,6 +18,7 @@ import static sop.external.JUtils.arrayStartsWith;
 import static sop.external.JUtils.assertArrayStartsWith;
 import static sop.external.JUtils.assertAsciiArmorEquals;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalArmorDearmorRoundTripTest extends AbstractExternalSOPTest {
 
     private static final String BEGIN_PGP_PRIVATE_KEY_BLOCK = "-----BEGIN PGP PRIVATE KEY BLOCK-----\n";
diff --git a/external-sop/src/test/java/sop/external/ExternalDecryptWithSessionKeyTest.java b/external-sop/src/test/java/sop/external/ExternalDecryptWithSessionKeyTest.java
index 7a5e4f6..8a7ff56 100644
--- a/external-sop/src/test/java/sop/external/ExternalDecryptWithSessionKeyTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalDecryptWithSessionKeyTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.ByteArrayAndResult;
@@ -17,6 +18,7 @@ import java.nio.charset.StandardCharsets;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalDecryptWithSessionKeyTest extends AbstractExternalSOPTest {
 
     private static final String CIPHERTEXT = "-----BEGIN PGP MESSAGE-----\n" +
diff --git a/external-sop/src/test/java/sop/external/ExternalDetachedSignVerifyRoundTripTest.java b/external-sop/src/test/java/sop/external/ExternalDetachedSignVerifyRoundTripTest.java
index 8e87b00..ddee99a 100644
--- a/external-sop/src/test/java/sop/external/ExternalDetachedSignVerifyRoundTripTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalDetachedSignVerifyRoundTripTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.SOP;
@@ -21,6 +22,7 @@ import static org.junit.jupiter.api.Assertions.assertThrows;
 import static sop.external.JUtils.assertArrayStartsWith;
 import static sop.external.JUtils.assertSignedBy;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalDetachedSignVerifyRoundTripTest extends AbstractExternalSOPTest {
 
     private static final String BEGIN_PGP_SIGNATURE = "-----BEGIN PGP SIGNATURE-----\n";
diff --git a/external-sop/src/test/java/sop/external/ExternalEncryptDecryptRoundTripTest.java b/external-sop/src/test/java/sop/external/ExternalEncryptDecryptRoundTripTest.java
index 2b505a4..4692f21 100644
--- a/external-sop/src/test/java/sop/external/ExternalEncryptDecryptRoundTripTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalEncryptDecryptRoundTripTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.ByteArrayAndResult;
@@ -26,6 +27,7 @@ import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalEncryptDecryptRoundTripTest extends AbstractExternalSOPTest {
 
     @ParameterizedTest
diff --git a/external-sop/src/test/java/sop/external/ExternalExtractCertTest.java b/external-sop/src/test/java/sop/external/ExternalExtractCertTest.java
index 39a661b..19866ee 100644
--- a/external-sop/src/test/java/sop/external/ExternalExtractCertTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalExtractCertTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.SOP;
@@ -17,6 +18,7 @@ import static sop.external.JUtils.arrayStartsWith;
 import static sop.external.JUtils.assertArrayStartsWith;
 import static sop.external.JUtils.assertAsciiArmorEquals;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalExtractCertTest extends AbstractExternalSOPTest {
 
     private static final String BEGIN_PGP_PUBLIC_KEY_BLOCK = "-----BEGIN PGP PUBLIC KEY BLOCK-----\n";
diff --git a/external-sop/src/test/java/sop/external/ExternalGenerateKeyTest.java b/external-sop/src/test/java/sop/external/ExternalGenerateKeyTest.java
index 7839c60..2525014 100644
--- a/external-sop/src/test/java/sop/external/ExternalGenerateKeyTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalGenerateKeyTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.SOP;
@@ -15,6 +16,7 @@ import java.nio.charset.StandardCharsets;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static sop.external.JUtils.assertArrayStartsWith;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalGenerateKeyTest extends AbstractExternalSOPTest {
 
     private static final Charset UTF8 = StandardCharsets.UTF_8;
diff --git a/external-sop/src/test/java/sop/external/ExternalInlineSignDetachVerifyRoundTripTest.java b/external-sop/src/test/java/sop/external/ExternalInlineSignDetachVerifyRoundTripTest.java
index a1e84b1..bc77534 100644
--- a/external-sop/src/test/java/sop/external/ExternalInlineSignDetachVerifyRoundTripTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalInlineSignDetachVerifyRoundTripTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.ByteArrayAndResult;
@@ -20,6 +21,7 @@ import static org.junit.jupiter.api.Assertions.assertFalse;
 import static sop.external.JUtils.arrayStartsWith;
 import static sop.external.JUtils.assertArrayStartsWith;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalInlineSignDetachVerifyRoundTripTest extends AbstractExternalSOPTest {
 
     private static final byte[] BEGIN_PGP_SIGNATURE = "-----BEGIN PGP SIGNATURE-----\n".getBytes(StandardCharsets.UTF_8);
diff --git a/external-sop/src/test/java/sop/external/ExternalInlineSignVerifyTest.java b/external-sop/src/test/java/sop/external/ExternalInlineSignVerifyTest.java
index e6ee329..22916d6 100644
--- a/external-sop/src/test/java/sop/external/ExternalInlineSignVerifyTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalInlineSignVerifyTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.ByteArrayAndResult;
@@ -22,6 +23,7 @@ import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static sop.external.JUtils.assertSignedBy;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalInlineSignVerifyTest extends AbstractExternalSOPTest {
 
     private static final String BEGIN_PGP_MESSAGE = "-----BEGIN PGP MESSAGE-----\n";
diff --git a/external-sop/src/test/java/sop/external/ExternalVersionTest.java b/external-sop/src/test/java/sop/external/ExternalVersionTest.java
index 0415d03..4b1f87c 100644
--- a/external-sop/src/test/java/sop/external/ExternalVersionTest.java
+++ b/external-sop/src/test/java/sop/external/ExternalVersionTest.java
@@ -4,6 +4,7 @@
 
 package sop.external;
 
+import org.junit.jupiter.api.condition.EnabledIf;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import sop.SOP;
@@ -12,6 +13,7 @@ import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+@EnabledIf("sop.external.AbstractExternalSOPTest#hasBackends")
 public class ExternalVersionTest extends AbstractExternalSOPTest {
 
     @ParameterizedTest