LUCENE-7009: Add expectThrows utility to LuceneTestCase

lucene/CHANGES.txt

@@ -110,6 +110,12 @@ Changes in Runtime Behavior
   and codec components are no longer allowed to use this extension
   (Robert Muir, Mike McCandless)
 
+Tests
+
+* LUCENE-7009: Add expectThrows utility to LuceneTestCase. This uses a lambda
+  expression to encapsulate a statement that is expected to throw an exception.
+  (Ryan Ernst)
+
 ======================= Lucene 5.5.0 =======================
 
 New Features

lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java

@@ -64,6 +64,7 @@ import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.logging.Logger;
 
+import junit.framework.AssertionFailedError;
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.document.Document;
@@ -2597,6 +2598,27 @@ public abstract class LuceneTestCase extends Assert {
     }
   }
 
+  /** A runnable that can throw any checked exception. */
+  @FunctionalInterface
+  public interface ThrowingRunnable {
+    void run() throws Throwable;
+  }
+
+  /** Checks a specific exception class is thrown by the given runnable, and returns it. */
+  public static <T extends Throwable> T expectThrows(Class<T> expectedType, ThrowingRunnable runnable) {
+    try {
+      runnable.run();
+    } catch (Throwable e) {
+      if (expectedType.isInstance(e)) {
+        return expectedType.cast(e);
+      }
+      AssertionFailedError assertion = new AssertionFailedError("Unexpected exception type, expected " + expectedType.getSimpleName());
+      assertion.initCause(e);
+      throw assertion;
+    }
+    throw new AssertionFailedError("Expected exception " + expectedType.getSimpleName());
+  }
+
   /** Returns true if the file exists (can be opened), false
    *  if it cannot be opened, and (unlike Java's
    *  File.exists) throws IOException if there's some