I have a VF Page that simply displays two graphs that I have created for display. The controller for this is an extension. I am not great with Test Code Coverage, so I was hoping for some help. My class is below:
public with sharing class TestResultGraphConroller {

    public string strTrial;
 
    public TestResultGraphConroller(ApexPages.StandardController stdController){
        strTrial = ApexPages.currentPage().getParameters().get('Id');
    }
   
   
    public String getTimeVolume(){
        return getTimeVolume(null);
    }
   
    public String getTimeVolume(List<Id> ids){
        GoogleViz gv = new GoogleViz();             
        gv.cols = new list<GoogleViz.col> {
            new GoogleViz.Col('col2','Interval','number'),
            new GoogleViz.Col('col1','Channel Volume','number')
            };
        decimal interval = 0;
       
        for(Trial__c tv : [Select Id, DisplayChannelVolume__c, TimeZeroOffset__c from Trial__c where Id = :strTrial limit 1])
        {
          String x = tv.DisplayChannelVolume__c;
          List<String> channelvolumevalues = x.split(' ');
         
          interval = tv.TimeZeroOffset__c;
         
          for(String cv: channelvolumevalues)
          {
            GoogleViz.row r = new GoogleViz.row();
            r.cells.add ( new GoogleViz.cell( interval));//interval
            r.cells.add ( new GoogleViz.cell( cv ));//X-Axis
            gv.addRow( r );
            interval = interval + .04;
            }
        }
        return gv.toJsonString();
    }
   
    public String getFlowVolume(){
        return getFlowVolume(null);
    }
   
  public String getFlowVolume(List<Id> ids){
        GoogleViz gv = new GoogleViz();             
        gv.cols = new list<GoogleViz.col> {
            new GoogleViz.Col('col1','Channel Volume','number'),
            new GoogleViz.col('col2','Channel Flow','number')   
            };             
              
        for(Trial__c tfv : [Select Id, DisplayChannelFlow__c, DisplayChannelVolume__c From Trial__c where Id = :strTrial limit 1])
        {                                                         
            String x = tfv.DisplayChannelVolume__c;
            String y = tfv.DisplayChannelFlow__c;
            List<String> channelvolumevalues = x.split(' ');
            List<String> channelflowvalues = y.split(' ');
           
            for(integer i=0; i< channelvolumevalues.size(); i++) //iterate using an integer
            {
              String cv = channelvolumevalues[i]; //get the element at the ith position
              String cf = channelflowvalues[i]; //get matching element at the ith position
              GoogleViz.row r = new GoogleViz.row();
              r.cells.add ( new GoogleViz.cell( cv ));//Y-Axis
              r.cells.add ( new GoogleViz.cell( cf ));//X-Axis
              gv.addRow( r );
            }
        }

        return gv.toJsonString();
    }
}

And my Test Class:

@isTest
public class testTestResultGraphConroller {

    private static testMethod void testTestResultGraphConroller() {
    
     Trial_Session__c tts1 = new Trial_Session__c();
     tts1.Lab__c = 'Test1';
    
     insert tts1;
    
     Trial__c tt1 = new Trial__c();
        tt1.Channel_Flow__c = '0.123456789 0.223456789';
        tt1.Channel_Flow_2__c = '0.423456789 0.523456789 0.623456789';    
     tt1.Channel_Volume__c = '0.123456789 0.223456789';
        tt1.Channel_Volume_2__c = '0.423456789 0.523456789 0.623456789';    
     tt1.DisplayChannelFlow__c = '-0.01114792 0.0204 0.051 0.0714 0.0918';
     tt1.DisplayChannelVolume__c = '0.9639643 0.9641174 0.9645764 0.9652394 0.9661258';
     tt1.TimeZeroOffset__c = 12.0;
     tt1.Trial_Session__c = tts1.Id;
    
     insert tt1;   
    
     Test.startTest();
    
     ApexPages.currentPage().getParameters().put('Id',tts1.Id);
     ApexPages.Standardcontroller stdTrialSession = new ApexPages.Standardcontroller(tts1);
     TestResultGraphConroller trgc = new TestResultGraphConroller(stdTrialSession);
    
     trgc.getFlowVolume();
     trgc.getFlowVolume(??????);
     trgc.getTimeVolume();
     trgc.getTimeVolume(??????);
    
     Test.stopTest();
    }
}

I am not sure what to write into the ??????'s

Thank you for your help.