<apex:page sidebar="false" controller="GetPattern">
        <apex:pageBlock title="Pattern">
            <apex:form>
				<apex:selectList value="{!filterId}" size="1">
					<apex:actionSupport event="onchange" action="{!processRequests}"  rerender="PB1"/>
					<apex:selectOptions value="{!items}"/>
				</apex:selectList>
            </apex:form>
         </apex:pageBlock>         
		 
         <apex:pageBlock title="Pattern Summary" id="PB1">
            <apex:pageBlockTable value="{!categorylist}" var="cat">
               <apex:column headerValue="Name" value="{!cat.Name}"/>
               <apex:column headerValue="Category A" value="{!cat.CategoryA__c}"/>
               <apex:column headerValue="Category B" value="{!cat.CategoryB__c}"/>
            </apex:pageBlockTable>
         </apex:pageBlock>         
</apex:page>

public class GetPattern
{
    public string FilterId{get;set;}
    public List<Pattern__c> categorylist {get; set;}
    public GetPattern()
    {
       categorylist = new List<Pattern__c>();
    }
    
    public PageReference processRequests()
    {
        categorylist.clear();
        if(FilterId !='' && FilterId != null)
        {
            categorylist = [select Name,CategoryA__c,CategoryB__C from Pattern__c where Name = :FilterId ];
        }
        else
        {
            categorylist = [select Name,CategoryA__c,CategoryB__C from Pattern__c limit 1000 ];
        }
        return null;
    }

    public List<SelectOption> getItems() 
    {
        List<SelectOption> options = new List<SelectOption>();
        List<Pattern__c> categorylist = [select Name,CategoryA__c,CategoryB__C from Pattern__c limit 1000];
        Set<String> patterns = new Set<String>();
        
        for(Pattern__c pattern :categorylist)
        {
            if(patterns.contains(pattern.Name))
            {
                options.add(new SelectOption(pattern.Name,pattern.Name ));
                patterns.add(pattern.Name);
            }        
        }    
        return options;
    }

}

@isTest 
public class GetPatternTest 
{
	static testMethod void GetPatternT() 
	{
		List<Pattern__c> lstPattern = new List<Pattern__c>();
		Pattern__c p1 = new Pattern__c();
		p1.Name = 'Pattern A';
		P1.CategoryA__c ='Code';
		P1.CategoryB__c ='ItemCode';
		lstPattern.add(p1);

		Pattern__c p2 = new Pattern__c();
		p2.Name = 'Pattern B';
		P2.CategoryA__c ='Code';
		P2.CategoryB__c ='ItemCode';
		lstPattern.add(p2);

		insert lstPattern;

		Test.StartTest(); 
			GetPattern contrl = new GetPattern();
			List<SelectOption> lst = contrl.getItems();
			contrl.FilterId ='Pattern A';
			contrl.processRequests();
		Test.StopTest();
		
	}
 
}