Add support for @FailsWith to assert errorMessage

docs/release_notes.adoc

@@ -19,6 +19,7 @@ include::include.adoc[]
 * Add `IStatelessAnnotationDrivenExtension` to allow a single extension instance to be reused across all specifications spockPull:2055[]
 * Add new well-known versions to `Jvm` helper to support versions up to 29 spockPull:2057[]
 ** Built-in extensions have been updated to use this new interface where applicable.
+* Add support for `@FailsWith` to assert exception message spockIssue:2039[]
 * Improve `@Timeout` extension will now use virtual threads if available spockPull:1986[]
 * Improve mock argument matching, types constraints or arguments in interactions can now handle primitive types like `_ as int` spockIssue:1974[]
 * Improve `verifyEach` to accept an optional second index parameter for the assertion block closure spockPull:2043[]

spock-core/src/main/java/org/spockframework/runtime/extension/builtin/FailsWithInterceptor.java

@@ -18,8 +18,12 @@
 
 import org.spockframework.runtime.*;
 import org.spockframework.runtime.extension.*;
+import org.spockframework.runtime.model.TextPosition;
+
 import spock.lang.FailsWith;
 
+import java.util.Arrays;
+
 /**
  *
  * @author Peter Niederwieser
@@ -44,7 +48,20 @@ public void intercept(IMethodInvocation invocation) throws Throwable {
   }
 
   private boolean checkException(Throwable t) {
+    if(matchesException(t)) {
+      if (!failsWith.expectedMessage().isEmpty() && !failsWith.expectedMessage().equals(t.getMessage())) {
+        throw new ConditionNotSatisfiedError(new Condition(
+            Arrays.asList(t, t.getMessage(), failsWith.expectedMessage()),
+            "e.value == expectedMessage",
+            TextPosition.create(-1, -1), null, null, null));
+      }
+      return true;
+    }
+    return false;
+  }
+
+  private boolean matchesException(Throwable t) {
     return failsWith.value().isInstance(t)
-      || (t instanceof ConditionFailedWithExceptionError && failsWith.value().isInstance(t.getCause()));
+        || (t instanceof ConditionFailedWithExceptionError && failsWith.value().isInstance(t.getCause()));
   }
 }

spock-core/src/main/java/spock/lang/FailsWith.java

@@ -50,4 +50,13 @@
    * @return the reason for the failure
    */
   String reason() default "unknown";
+
+  /**
+   * The expected message of the exception.
+   * <p>
+   * If the value is empty, the message is not checked.
+   *
+   * @since 2.4
+   */
+  String expectedMessage() default "";
 }

spock-specs/src/test/groovy/org/spockframework/smoke/extension/FailsWithExtension.groovy

@@ -22,19 +22,24 @@ import org.spockframework.runtime.InvalidSpecException
 import spock.lang.FailsWith
 import spock.lang.Specification
 
+import org.spockframework.runtime.SpockComparisonFailure
+
 /**
  *
  * @author Peter Niederwieser
  */
-class FailsWithOnMethod extends Specification {
+class FailsWithOnMethod extends EmbeddedSpecification {
   @FailsWith(IndexOutOfBoundsException)
   def ex1() {
     given:
     def foo = []
     foo.get(0)
   }
 
-  @FailsWith(Exception)
+  @FailsWith(
+      value = Exception,
+      expectedMessage = "Index 0 out of bounds for length 0"
+  )
   def ex2() {
     given:
     def foo = []
@@ -45,6 +50,33 @@ class FailsWithOnMethod extends Specification {
     expect: true
   }
 
+  def "@FailsWith can assert exception message"() {
+    when:
+    runner.runSpecBody """
+  @FailsWith(
+      value = Exception,
+      expectedMessage = "Index 1 out of bounds for length 1"
+  )
+  def foo() {
+    given:
+    def foo = []
+    foo.get(0)
+  }
+    """
+
+    then:
+    SpockComparisonFailure e = thrown()
+    def expected = """Condition not satisfied:
+
+e.value == expectedMessage
+| |        |
+| |        Index 1 out of bounds for length 1
+| Index 0 out of bounds for length 0
+java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0"""
+
+    e.message.startsWith(expected)
+
+  }
 
   @FailsWith(ConditionFailedWithExceptionError)
   def "can handle ConditionFailedWithExceptionError"() {
@@ -117,4 +149,3 @@ class MySpec extends Specification {
     e.message == "@FailsWith needs to refer to an exception type, but does refer to 'java.util.List'"
   }
 }
-