fix: Implement test ID truncation in MdcLoggingExtension

src/main/java/com/pdsl/junit/jupiter/extension/extension/LoggingConstants.java

@@ -2,6 +2,8 @@
 
 public final class LoggingConstants {
     public static final String TEST_ID_KEY = "testId";
+    public static final String TEST_ID_DELIMITER = "_";
+    public static final int MAX_TEST_ID_LENGTH = 120;
 
     private LoggingConstants() {
     }

src/main/java/com/pdsl/junit/jupiter/extension/extension/MdcLoggingExtension.java

@@ -1,5 +1,6 @@
 package com.pdsl.junit.jupiter.extension.extension;
 
+import org.checkerframework.checker.nullness.qual.NonNull;
 import org.junit.jupiter.api.extension.AfterEachCallback;
 import org.junit.jupiter.api.extension.BeforeEachCallback;
 import org.junit.jupiter.api.extension.ExtensionContext;
@@ -26,17 +27,8 @@ public class MdcLoggingExtension implements BeforeEachCallback, AfterEachCallbac
      */
     @Override
     public void beforeEach(ExtensionContext context) {
-        String testClassName = context.getRequiredTestClass().getSimpleName();
-        String testMethodName = context.getRequiredTestMethod().getName();
-        // For @TestTemplate or parameterized tests, getDisplayName() returns the unique invocation name
-        String displayName = context.getDisplayName();
-
-        // Sanitize the display name to construct a safe filename
-        String sanitizedDisplayName = displayName.replaceAll("[^a-zA-Z0-9_\\-]", "_")
-                .replaceAll("_+", "_")
-                .trim();
-        // Construct a unique Test ID
-        String testId = String.format("%s_%s_%s", testClassName, testMethodName, sanitizedDisplayName);
+        String testId = buildUniqTestIdValue(context);
+        testId = truncateTestId(testId);
 
         // Put the unique identifier into MDC
         MDC.put(LoggingConstants.TEST_ID_KEY, testId);
@@ -55,4 +47,44 @@ public void afterEach(ExtensionContext context) throws Exception {
         // Remove the key to prevent context leakage between threads or test executions
         MDC.remove(LoggingConstants.TEST_ID_KEY);
     }
+
+    /**
+     * Constructs a unique, sanitized test identifier string from the extension context.
+     *
+     * <p>This method combines the test class simple name, the test method name, and a
+     * sanitized version of the display name (removing any characters not safe for filenames).
+     *
+     * @param context the extension context of the current test
+     * @return the constructed unique test ID string
+     */
+    private static @NonNull String buildUniqTestIdValue(ExtensionContext context) {
+        String testClassName = context.getRequiredTestClass().getSimpleName();
+        String testMethodName = context.getRequiredTestMethod().getName();
+        // For @TestTemplate or parameterized tests, getDisplayName() returns the unique invocation name
+        String displayName = context.getDisplayName();
+
+        String sanitizedDisplayName = displayName.replaceAll("[^a-zA-Z0-9_\\-]", LoggingConstants.TEST_ID_DELIMITER)
+                .replaceAll(LoggingConstants.TEST_ID_DELIMITER + "+", LoggingConstants.TEST_ID_DELIMITER)
+                .trim();
+        return String.join(LoggingConstants.TEST_ID_DELIMITER, testClassName, testMethodName, sanitizedDisplayName);
+    }
+
+    /**
+     * Limits the length of the constructed test ID to prevent filesystem issues.
+     *
+     * <p>If the test ID is longer than the limit defined in {@link LoggingConstants#MAX_TEST_ID_LENGTH}, 
+     * it is truncated. A hexadecimal hash suffix generated from the original test ID is appended 
+     * to guarantee uniqueness and prevent collisions.
+     *
+     * @param testId the full constructed test ID to truncate
+     * @return the truncated test ID (guaranteed to be under {@link LoggingConstants#MAX_TEST_ID_LENGTH} characters)
+     */
+    private static @NonNull String truncateTestId(String testId) {
+        if (testId.length() > LoggingConstants.MAX_TEST_ID_LENGTH) {
+            String hash = Integer.toHexString(testId.hashCode());
+            int truncateIndex = LoggingConstants.MAX_TEST_ID_LENGTH - hash.length() - LoggingConstants.TEST_ID_DELIMITER.length();
+            return testId.substring(0, truncateIndex) + LoggingConstants.TEST_ID_DELIMITER + hash;
+        }
+        return testId;
+    }
 }

src/test/java/com/pdsl/junit/jupiter/extension/MdcLoggingExtensionTest.java

@@ -82,6 +82,36 @@ public void beforeEach_withSpecialCharactersDisplayName_sanitizesAndPutsFormatte
         assertThat(MDC.get(LoggingConstants.TEST_ID_KEY)).isEqualTo(expectedTestId);
     }
 
+    @Test
+    public void beforeEach_withTooLongTestId_truncatesAndAppendsHash() throws NoSuchMethodException {
+        // Arrange
+        Class<?> testClass = DummyTestClass.class;
+        Method testMethod = DummyTestClass.class.getDeclaredMethod("dummyMethod");
+        // Create an exceptionally long display name (e.g. 200 characters)
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < 20; i++) {
+            sb.append("veryLongDisplayNameSegment");
+        }
+        String displayName = sb.toString();
+
+        when(mockContext.getRequiredTestClass()).thenAnswer(invocation -> testClass);
+        when(mockContext.getRequiredTestMethod()).thenReturn(testMethod);
+        when(mockContext.getDisplayName()).thenReturn(displayName);
+
+        // Act
+        extension.beforeEach(mockContext);
+
+        // Assert
+        String actualTestId = MDC.get(LoggingConstants.TEST_ID_KEY);
+        assertThat(actualTestId).isNotNull();
+        assertThat(actualTestId.length()).isEqualTo(LoggingConstants.MAX_TEST_ID_LENGTH);
+
+        // Calculate expected hash for full testId before truncation
+        String fullTestId = String.join(LoggingConstants.TEST_ID_DELIMITER, testClass.getSimpleName(), testMethod.getName(), displayName);
+        String expectedHash = Integer.toHexString(fullTestId.hashCode());
+        assertThat(actualTestId).endsWith(LoggingConstants.TEST_ID_DELIMITER + expectedHash);
+    }
+
     @Test
     public void afterEach_clearsTestIdFromMdc() throws Exception {
         // Arrange