SFDCRules - http://www.jitendrazaa.com/blog/salesforce/sfdcrules-simple-yet-powerful-rule-engine-for-salesforce/

TestRuleEngine.cls

/**
* @Author : Jitendra Zaa
* @Date : 25-March-2017
* @Desc : Classes to implement BPM (Business Process Management ) rule engine
*
* @Known Issue : 1. String values cannot have spaces
* : 3. All operators should have spaces , before and after, else it would raise an error.
* : There is no code written yet to auto format expression.
* */
@isTest
public class TestRuleEngine {

static Map<String, String> initBindings() {
Map<String, String> bindings = new Map<String, String>();
bindings.put('Val1'.toLowerCase(), '100');
bindings.put('Val2'.toLowerCase(), '200');
bindings.put('Val3'.toLowerCase(), '300');
bindings.put('Val4'.toLowerCase(), 'RuleEngine');
bindings.put('Val5'.toLowerCase(), 'false');
return bindings;
}

static Operations initOperations() {
Operations opObj = Operations.getInstance();
opObj.registerOperation(OperationFactory.getInstance('&&'));
opObj.registerOperation(OperationFactory.getInstance('=='));
opObj.registerOperation(OperationFactory.getInstance('!='));
opObj.registerOperation(OperationFactory.getInstance('||'));
opObj.registerOperation(OperationFactory.getInstance('('));
opObj.registerOperation(OperationFactory.getInstance(')'));
opObj.registerOperation(OperationFactory.getInstance('<'));
opObj.registerOperation(OperationFactory.getInstance('<=')); 
opObj.registerOperation(OperationFactory.getInstance('>'));
opObj.registerOperation(OperationFactory.getInstance('>='));
return opObj;
}

public static testmethod void condition_Test_All_Operators(){

Map<String, String> bindings = initBindings();
Operations opObj = initOperations();

//declaration
String expr ;
Rule r = new Rule() ;
Boolean retVal;

expr = 'Val1 != 800' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val1 != 800 || ( Val2 != 200 && Val3 != 200 )' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val1 &amp;lt; 110' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val1 &amp;lt;= 100' ; 
r.setExpression(expr); 
retVal = r.eval(bindings) ; 
System.assertEquals(true, retVal); 
expr = 'Val2 > 110.5' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val2 >= 110' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val3 == 300' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val3 == 300.0' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val4 == RuleEngine' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val4 == "ruleengine"' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val4 == ruleEngine' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val5 == false' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

//As below comparision is not valid, return false
expr = 'Val5 > false' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(false, retVal);

//As below comparision is not valid, return false
expr = 'Val5 >= false' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(false, retVal);

//As below comparision is not valid, return false
expr = 'Val5 < false' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(false, retVal);

//As below comparision is not valid, return false
expr = 'Val5 <= false' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(false, retVal);

expr = 'Val1 == 100 || ( Val2 == 300 && Val3 == 200 && Val4 == ruleEngine )' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val1 == 300 || ( Val2 == 300 && Val3 == 200 && Val4 == ruleEngine )' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(false, retVal);

expr = 'Val1 == 300 || ( Val2 == 300 ) && ( Val3 == 200 ) && ( Val4 == ruleEngines )' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(false, retVal);

expr = 'Val1 == 300 || ( ( Val2 == 300 ) && ( Val3 == 200 ) && ( Val4 == ruleEngines && Val1 == 120 ) ) || Val1 == 100' ;
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val1 == 1500 || Val1 == 1400 || Val1 == 1300 || Val1 == 1200 || Val1 == 1100 || Val1 == 1200 || Val1 == 1100 || Val1 == 1000'+
' || Val1 == 900 || Val1 == 800 || Val1 == 700 || Val1 == 600 || Val1 == 500 || Val1 == 400 || Val1 == 300 || Val1 == 200 || Val1 == 100';
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

expr = 'Val1 == 1500 && Val1 == 1400 && Val1 == 1300 && Val1 == 1200 && Val1 == 1100 && Val1 == 1200 && Val1 == 1100 && Val1 == 1000'+
' && Val1 == 900 && Val1 == 800 && Val1 == 700 && Val1 == 600 && Val1 == 500 && Val1 == 400 && Val1 == 300 && Val1 == 200 && Val1 == 100';
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(false, retVal);

//Test comma separated value
expr = 'Val1 == 1,2,3,4,5,6,7,100';
r.setExpression(expr);
retVal = r.eval(bindings) ;
System.assertEquals(true, retVal);

}
}