基于Predictive Parsing的ABNF语法分析器(4)——准备单元测试代码

单元测试的重要性是不言而喻的,对于ABNF的例子来说,通过单元测试除了可以发现程序的BUG之外,还可以发现预测解析器能够支持哪些情况下的文法,以及那些情况下解析器无能为力(所谓FEATURE,嘿嘿)。

我在这个项目中使用JUnit来做单元测试,先来看一段最简单的测试代码:

 

/*

    This file is one of the component a Context-free Grammar Parser Generator,

    which accept a piece of text as the input, and generates a parser

    for the inputted context-free grammar.

    Copyright (C) 2013, Junbiao Pan (Email: [email protected])



    This program is free software: you can redistribute it and/or modify

    it under the terms of the GNU General Public License as published by

    the Free Software Foundation, either version 3 of the License, or

    any later version.



    This program is distributed in the hope that it will be useful,

    but WITHOUT ANY WARRANTY; without even the implied warranty of

    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    GNU General Public License for more details.



    You should have received a copy of the GNU General Public License

    along with this program.  If not, see <http://www.gnu.org/licenses/>.

 */



//  SP             =  %x20

	protected String SP() throws IOException, MatchException {

        assertMatch(is.peek(), 0x20);

        int value = is.read();

        return String.valueOf((char)value);

	}



    @Test

    public void testSP() throws Exception {

        Tester<String> tester = new Tester<String>() {

            @Override

            public String test(AbnfParser parser) throws MatchException, IOException {

                return parser.SP();

            }

        };

//    测试用例1:字符串输入流为两个空格的情况(结果应该是只匹配第一个空格)

        Assert.assertEquals(String.valueOf((char)0x20), AbnfParserFactory.newInstance(new char[] {0x20, 0x20}).SP());

//    测试用例2:字符串输入流为空的情况

        Assertion.assertMatchException("", tester, 1, 1);

//    测试用例3:字符串输入流为回车(0x0D)的情况

        Assertion.assertMatchException("" + (char)0x0D, tester, 1, 1);



    }

为图方便我把被测代码和测试代码都放到一起了,testSP()函数用来测试SP()函数的功能是否满足。SP()是用来解析空格输入的函数,即当输入流的下一个字符是空格时,返回这个空格,否则抛出一个匹配异常MatchException。

 

单元测试的关键要素(输入参数)是测试用例(比如字符串输入流)和期望结果,在每一个测试用例中,都要调用一次被测函数,然后检查输出结果是否与预期结果一直。这里面有一部分代码是要重复使用的,为了偷懒(以免要大段大段的复制粘贴代码),抽象出Tester测试器接口和Assertion断言类。

Tester测试器接口的代码如下:

 

public interface Tester<E> {

    public abstract E test(AbnfParser parser) throws MatchException, IOException, CollisionException;

}

Tester接口只有一个test函数。例如在测试testSP函数中,定义了一个Tester的匿名类,在这个类的test函数中调用被测函数。有了Tester接口,我们在不同的测试用例下只需要指定一个Tester的实例就行,而不需要每次都调用被测函数。

 

再来看看Assertion断言类,这也是一个提供方便的类,这个类提供了若干个方法,支持不同情况下调用Tester实例,并将测试结果与期望结果相比较,如果不一致则抛出异常。

 

/*

    This file is one of the component a Context-free Grammar Parser Generator,

    which accept a piece of text as the input, and generates a parser

    for the inputted context-free grammar.

    Copyright (C) 2013, Junbiao Pan (Email: [email protected])



    This program is free software: you can redistribute it and/or modify

    it under the terms of the GNU General Public License as published by

    the Free Software Foundation, either version 3 of the License, or

    any later version.



    This program is distributed in the hope that it will be useful,

    but WITHOUT ANY WARRANTY; without even the implied warranty of

    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    GNU General Public License for more details.



    You should have received a copy of the GNU General Public License

    along with this program.  If not, see <http://www.gnu.org/licenses/>.

 */

import junit.framework.Assert;

import java.io.IOException;



public class Assertion {

//    断言匹配

    public static void assertMatch(String input, Tester tester, Object expectedOutput, int expectedPos, int expectedLine) throws MatchException, IOException, CollisionException {



//    根据字符串输入流创建一个AbnfParser实例

        AbnfParser parser = AbnfParserFactory.newInstance(input);



//    调用Tester接口实例进行测试

        Object output = tester.test(parser);



//    判断测试结果是否与期望结果一致

        if (output == null && expectedOutput != null) Assert.fail();

        if (output != null && expectedOutput == null) Assert.fail();

        if (output != null && expectedOutput != null) Assert.assertEquals(expectedOutput, output);



//    判断输入流的指针位置是否与期望一致

        Assert.assertEquals(expectedPos, parser.getInputStream().getPos());

        Assert.assertEquals(expectedLine, parser.getInputStream().getLine());

    }



    public static void assertMatch(String input, Tester tester, int expectedPos, int expectedLine) throws MatchException, IOException, CollisionException {

        AbnfParser parser = AbnfParserFactory.newInstance(input);

        tester.test(parser);

        Assert.assertEquals(expectedPos, parser.getInputStream().getPos());

        Assert.assertEquals(expectedLine, parser.getInputStream().getLine());

    }



//    断言要抛出匹配异常

    public static void assertMatchException(String input, Tester tester, int expectedPos, int expectedLine) {

//    根据字符串输入流创建一个AbnfParser实例

        AbnfParser parser = AbnfParserFactory.newInstance(input);

        try {

//    调用测试函数

            tester.test(parser);

//    如果执行到这里(意味着测试函数没有抛出异常),则测试不通过

            Assert.fail();

        } catch (MatchException me) {

//    如果捕捉到匹配异常,则继续检查输入流的指针位置是否正确

            Assert.assertEquals(expectedPos, parser.getInputStream().getPos());

            Assert.assertEquals(expectedLine, parser.getInputStream().getLine());

        } catch (IOException e) {

//    其他异常表明测试不通过

            Assert.fail();

        } catch (CollisionException ce) {

//    其他异常表明测试不通过

            Assert.fail();

        }

    }



//    断言要抛出冲突异常(流程类似匹配异常,主要针对ABNF规则名重名的情况)

    public static void assertCollisionException(String input, Tester tester, int expectedPos, int expectedLine) {

        AbnfParser parser = AbnfParserFactory.newInstance(input);

        try {

            tester.test(parser);

            Assert.fail();

        } catch (MatchException me) {

            Assert.fail();

        } catch (IOException e) {

            Assert.fail();

        } catch (CollisionException ce) {

            Assert.assertEquals(expectedPos, parser.getInputStream().getPos());

            Assert.assertEquals(expectedLine, parser.getInputStream().getLine());

        }

    }

}

这里再补充说明一下AbnfParserFactory工厂类,这个类主要是为了方便将字符串转换为输入流并创建AbnfParser实例而写的,代码很简单:

/*

    This file is one of the component a Context-free Grammar Parser Generator,

    which accept a piece of text as the input, and generates a parser

    for the inputted context-free grammar.

    Copyright (C) 2013, Junbiao Pan (Email: [email protected])



    This program is free software: you can redistribute it and/or modify

    it under the terms of the GNU General Public License as published by

    the Free Software Foundation, either version 3 of the License, or

    any later version.



    This program is distributed in the hope that it will be useful,

    but WITHOUT ANY WARRANTY; without even the implied warranty of

    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    GNU General Public License for more details.



    You should have received a copy of the GNU General Public License

    along with this program.  If not, see <http://www.gnu.org/licenses/>.

 */



import java.io.ByteArrayInputStream;



public class AbnfParserFactory {

    public static AbnfParser newInstance(String prefix, String input) {

        return new AbnfParser(prefix, new ByteArrayInputStream(input.getBytes()));

    }

    public static AbnfParser newInstance(String input) {

        return new AbnfParser("", new ByteArrayInputStream(input.getBytes()));

    }

    public static AbnfParser newInstance(String prefix, char[] input) {

        return new AbnfParser(prefix, new ByteArrayInputStream(String.valueOf(input).getBytes()));

    }

    public static AbnfParser newInstance(char[] input) {

        return new AbnfParser("", new ByteArrayInputStream(String.valueOf(input).getBytes()));

    }

}

有了这个工厂类,单元测试的时候就方便多了,因为我们的测试用例可能是字符串、字符数组,这个工厂类能够帮助我们快速创建AbnfParser实例。

通过单元测试可以发现很多我们意想不到的情况,例如:

 

    //		        elements       =  alternation *c-wsp

    @Test

    public void testElements() throws Exception {

        Tester<Elements> tester = new Tester<Elements>() {

            @Override

            public Elements test(AbnfParser parser) throws MatchException, IOException {

                return parser.elements();

            }

        };



        String input;

        input = "A/B/C";

        Assertion.assertMatch(input, tester, AbnfParserFactory.newInstance(input).elements(), 6, 1);



//        TODO

        input = "A/B/C  ";

        Assertion.assertMatchException(input, tester, 8, 1);



    }

原来这个预测解析器无法处理对于输入的Alternation为“A/B/C ”即后面多一个空格的情形,具体的原因我们在后面的帖子里再慢慢分析吧。

 

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