diff --git a/codebase-graph-builder/src/test/java/org/hjug/graphbuilder/graphbuilder/Java25ParserFactoryTest.java b/codebase-graph-builder/src/test/java/org/hjug/graphbuilder/graphbuilder/Java25ParserFactoryTest.java
index 3c991a98..e875c6f0 100644
--- a/codebase-graph-builder/src/test/java/org/hjug/graphbuilder/graphbuilder/Java25ParserFactoryTest.java
+++ b/codebase-graph-builder/src/test/java/org/hjug/graphbuilder/graphbuilder/Java25ParserFactoryTest.java
@@ -103,6 +103,22 @@ void versionedVariantCreatesWorkingJava25Parser() throws Exception {
                         + parsed.get(0).getClass().getName());
     }
 
+    @DisplayName("T2: versioned variant falls back when the Java 25 parser is unavailable")
+    @EnabledForJreRange(min = JRE.JAVA_25)
+    @Test
+    void versionedVariantFallsBackWhenJava25ParserIsUnavailable() throws Exception {
+        Class<?> versionedFactory = loadVersionedFactoryWithoutJava25Parser();
+
+        Object result = assertDoesNotThrow(
+                () -> versionedFactory.getMethod("createJava25Parser").invoke(null),
+                "The versioned factory must contain parser linkage failures");
+
+        assertInstanceOf(Optional.class, result);
+        assertTrue(
+                ((Optional<?>) result).isEmpty(),
+                "A missing Java25Parser must return an empty Optional so the caller can use its standard fallback");
+    }
+
     @DisplayName("T3: versioned and base variants expose identical public API (JEP 238 parity)")
     @EnabledForJreRange(min = JRE.JAVA_25)
     @Test
@@ -122,6 +138,14 @@ void versionedVariantExposesIdenticalPublicApi() throws Exception {
      * inactive).
      */
     private static Class<?> loadVersionedFactory() throws Exception {
+        return loadVersionedFactory(false);
+    }
+
+    private static Class<?> loadVersionedFactoryWithoutJava25Parser() throws Exception {
+        return loadVersionedFactory(true);
+    }
+
+    private static Class<?> loadVersionedFactory(boolean hideJava25Parser) throws Exception {
         assumeTrue(
                 Files.exists(VERSIONED_CLASSES_DIR.resolve(VERSIONED_CLASS_RELATIVE_PATH)),
                 "Versioned factory class only exists when built on JDK 25+");
@@ -138,7 +162,15 @@ protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundE
             }
         };
         URLClassLoader loader =
-                new URLClassLoader(new URL[] {VERSIONED_CLASSES_DIR.toUri().toURL()}, filteredParent);
+                new URLClassLoader(new URL[] {VERSIONED_CLASSES_DIR.toUri().toURL()}, filteredParent) {
+                    @Override
+                    protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+                        if (hideJava25Parser && name.equals("org.openrewrite.java.Java25Parser")) {
+                            throw new ClassNotFoundException(name);
+                        }
+                        return super.loadClass(name, resolve);
+                    }
+                };
         return Class.forName(FACTORY_FQN, false, loader);
     }
 
diff --git a/cost-benefit-calculator/src/test/java/org/hjug/cbc/CycleRankerGraphGenerationTest.java b/cost-benefit-calculator/src/test/java/org/hjug/cbc/CycleRankerGraphGenerationTest.java
index f743d0e4..02e1b6e5 100644
--- a/cost-benefit-calculator/src/test/java/org/hjug/cbc/CycleRankerGraphGenerationTest.java
+++ b/cost-benefit-calculator/src/test/java/org/hjug/cbc/CycleRankerGraphGenerationTest.java
@@ -9,6 +9,9 @@
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.NullAndEmptySource;
 
 /**
  * Verifies {@link CycleRanker#generateClassReferencesGraph(boolean, String)}
@@ -41,4 +44,46 @@ public void hello() {}
         assertNotNull(dto);
         assertTrue(dto.getClassReferencesGraph().containsVertex("com.example.Plain"));
     }
+
+    @ParameterizedTest
+    @NullAndEmptySource
+    @DisplayName("generateClassReferencesGraph rejects a missing source directory")
+    void rejectsMissingSourceDirectory(String repositoryPath) {
+        CycleRanker ranker = new CycleRanker(repositoryPath, tempDir.toString());
+
+        IllegalArgumentException exception = assertThrows(
+                IllegalArgumentException.class, () -> ranker.generateClassReferencesGraph(false, "src/test"));
+
+        assertEquals("Source directory cannot be null or empty", exception.getMessage());
+        assertNull(ranker.getCodebaseGraphDTO(), "A rejected request must not populate the graph DTO");
+    }
+
+    @ParameterizedTest(name = "excludeTests={0} should include custom test source={1}")
+    @CsvSource({"true, false", "false, true"})
+    @DisplayName("generateClassReferencesGraph forwards test exclusion configuration")
+    void forwardsTestExclusionConfiguration(boolean excludeTests, boolean expectTestSource) throws IOException {
+        writeJava(tempDir.resolve("src/main/java/com/example/ProductionClass.java"), "com.example", "ProductionClass");
+        writeJava(tempDir.resolve("custom-tests/com/example/FixtureClass.java"), "com.example", "FixtureClass");
+
+        CycleRanker ranker = new CycleRanker(tempDir.toString(), tempDir.toString());
+        CodebaseGraphDTO dto = ranker.generateClassReferencesGraph(excludeTests, "custom-tests");
+
+        assertTrue(dto.getClassReferencesGraph().containsVertex("com.example.ProductionClass"));
+        assertEquals(
+                expectTestSource,
+                dto.getClassReferencesGraph().containsVertex("com.example.FixtureClass"),
+                "The custom test source directory must follow the caller's exclusion setting");
+        assertSame(dto, ranker.getCodebaseGraphDTO(), "The generated DTO must remain available to cycle ranking");
+    }
+
+    private static void writeJava(Path path, String packageName, String className) throws IOException {
+        Files.createDirectories(path.getParent());
+        Files.writeString(
+                path,
+                """
+                package %s;
+                public class %s {}
+                """
+                        .formatted(packageName, className));
+    }
 }