maven-release-plugin/src/it/projects/prepare/fail-on-snapshots/verify.groovy

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
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def buildLog = new File(basedir,'build.log')
def nonReleased = buildLog.readLines()
                          .dropWhile{ !it.endsWith("Can't release project due to non released dependencies :") }
                          .drop(1)
                          .collect{ (it - '[ERROR]').trim() }
                          .takeWhile{ !it.startsWith("in project 'fail-on-snapshot'") } as Set

assert nonReleased == ['test:dependency:jar:1.0-SNAPSHOT:compile',
                       'test:dependency.test:jar:1.0-SNAPSHOT:test',
                       'test:extension:jar:1.0-SNAPSHOT',
                       'test:plugin:maven-plugin:1.0-SNAPSHOT:runtime',                                 
                       'test:report:maven-plugin:1.0-SNAPSHOT:runtime'] as Set