Asserter.java

/*
* Copyright 2016 Nabarun Mondal
* Licensed 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 under the License.
*
*/

package com.noga.njexl.lang.junit;

import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Map;

import com.noga.njexl.lang.JexlArithmetic;
import com.noga.njexl.lang.JexlException;
import com.noga.njexl.lang.MapContext;
import junit.framework.Assert;

import com.noga.njexl.lang.Expression;
import com.noga.njexl.lang.JexlContext;
import com.noga.njexl.lang.JexlEngine;
import com.noga.njexl.lang.JexlThreadedArithmetic;

/**
 * A utility class for performing JUnit based assertions using Jexl
 * expressions. This class can make it easier to do unit tests using
 * Jexl navigation expressions.
 *
 * @since 1.0
 */
public class Asserter extends Assert {
    /** variables used during asserts. */
    private final Map<String, Object> variables = new HashMap<String, Object>();
    /** context to use during asserts. */
    private final JexlContext context = new MapContext(variables);
    /** Jexl engine to use during Asserts. */
    private final JexlEngine engine;

    /**
     * 
     * Create an asserter.
     * @param jexl the JEXL engine to use
     */
    public Asserter(JexlEngine jexl) {
        engine = jexl;
    }

    /**
     * Retrieves the underlying JEXL engine.
     * @return the JEXL engine
     */
    public JexlEngine getEngine() {
        return engine;
    }

    /**
     * Retrieves the underlying JEXL context.
     * @return the JEXL context
     */
    public JexlContext getContext() {
        return context;
    }

    /**
     * Performs an assertion that the value of the given Jexl expression 
     * evaluates to the given expected value.
     * 
     * @param expression is the Jexl expression to evaluate
     * @param expected is the expected value of the expression
     * @throws Exception if the expression could not be evaluationed or an assertion
     * fails
     */
    public void assertExpression(String expression, Object expected) throws Exception {
        Expression exp = engine.createExpression(expression);
        Object value = exp.evaluate(context);
        if (expected instanceof BigDecimal) {
            JexlArithmetic jexla = engine.getArithmetic();
            assertTrue("expression: " + expression, ((BigDecimal) expected).compareTo(jexla.toBigDecimal(value)) == 0);
        } else {
            assertEquals("expression: " + expression, expected, value);
        }
    }

    /**
     * Performs an assertion that the expression fails throwing an exception.
     * If matchException is not null, the exception message is expected to match it as a regexp.
     * The engine is temporarily switched to strict * verbose to maximize error detection abilities.
     * @param expression the expression that should fail
     * @param matchException the exception message pattern
     * @throws Exception if the expression did not fail or the exception did not match the expected pattern
     */
    public void failExpression(String expression, String matchException) throws Exception {
        boolean[] flags = {engine.isLenient(), engine.isSilent()};
        try {
            if (engine.getArithmetic() instanceof JexlThreadedArithmetic) {
                engine.setLenient(false);
            }
            engine.setSilent(false);
            Expression exp = engine.createExpression(expression);
            exp.evaluate(context);
            fail("expression: " + expression);
        } catch (JexlException xjexl) {
            if (matchException != null && !xjexl.getMessage().matches(matchException)) {
                fail("expression: " + expression + ", expected: " + matchException + ", got " + xjexl.getMessage());
            }
        } finally {
            if (engine.getArithmetic() instanceof JexlThreadedArithmetic) {
                engine.setLenient(flags[0]);
            }
            engine.setSilent(flags[1]);
        }
    }

    /**
     * Puts a variable of a certain name in the context so that it can be used from
     * assertion expressions.
     * 
     * @param name variable name
     * @param value variable value
     */
    public void setVariable(String name, Object value) {
        variables.put(name, value);
    }

    /**
     * Removes a variable of a certain name from the context.
     * @param name variable name
     * @return variable value
     */
    public Object removeVariable(String name) {
        return variables.remove(name);
    }
}