Handle failures after closed transaction

We should not run `onError` of a transaction after the transaction
has been successfully closed.

Fixes #146

Author: pontusmelke

driver/src/main/java/org/neo4j/driver/internal/InternalSession.java

@@ -137,9 +137,13 @@ public Transaction beginTransaction()
             @Override
             public void run()
             {
-                currentTransaction.markAsRolledBack();
-                currentTransaction = null;
-                connection.onError( null );
+                //must check if transaction has been closed
+                if (currentTransaction != null)
+                {
+                    currentTransaction.markAsRolledBack();
+                    currentTransaction = null;
+                    connection.onError( null );
+                }
             }
         });
         return currentTransaction;

driver/src/test/java/org/neo4j/driver/v1/integration/TransactionIT.java

@@ -54,7 +54,7 @@ public void shouldRunAndCommit() throws Throwable
         // Then the outcome of both statements should be visible
         StatementResult result = session.run( "MATCH (n) RETURN count(n)" );
         long nodes = result.single().get( "count(n)" ).asLong();
-        assertThat( nodes, equalTo( 2l ) );
+        assertThat( nodes, equalTo( 2L ) );
     }
 
     @Test
@@ -70,7 +70,7 @@ public void shouldRunAndRollbackByDefault() throws Throwable
         // Then there should be no visible effect of the transaction
         StatementResult cursor = session.run( "MATCH (n) RETURN count(n)" );
         long nodes = cursor.single().get( "count(n)" ).asLong();
-        assertThat( nodes, equalTo( 0l ) );
+        assertThat( nodes, equalTo( 0L ) );
     }
 
     @Test
@@ -146,4 +146,22 @@ public void shouldHandleNullParametersGracefully()
 
     }
 
+    //See GH #146
+    @Test
+    public void shouldHandleFailureAfterClosingTransaction()
+    {
+        // GIVEN a successful query in a transaction
+        Transaction tx = session.beginTransaction();
+        StatementResult result = tx.run("CREATE (n) RETURN n");
+        result.consume();
+        tx.success();
+        tx.close();
+
+        // EXPECT
+        exception.expect( ClientException.class );
+
+        //WHEN running a malformed query in the original session
+        session.run("CREAT (n) RETURN n").consume();
+    }
+
 }