I created a VisualForce page to process CSV files for people to create leads. For some reason when I go to call the method for my test class to read the CSV file I am getting the error Non static method cannot be referenced from a static context: void UploadCSVController.ReadFromFile(). Is there certain ways you need to do this for a test class?

VP Page:

<apex:page lightningStylesheets="true" controller="UploadCSVController">
<h1 style="font-size:30px"><center>Automation Upload</center></h1><br/><br/>

<apex:form id="idForm">
    <apex:pageMessages /><br/><br/>

    <apex:pageBlock tabStyle="Lead" id="idInputBlock">
        <p style="height:13px; font-size:13px"><b>Set the first column of the CSV file as LastName Field:</b></p><br/>
        <apex:inputFile value="{!fileBody}" fileSize="{!fileSize}" fileName="{!fileName}" accept=".csv" contentType="text/csv" id="idInputFile"></apex:inputFile>                 
        <!-- Input File -->
        <apex:commandButton value="Upload File" action="{!ReadFromFile}" onclick="document.getElementById('actionStatusUP').style.display = 'inline';" />  
        <!-- Upload Button to upload file -->
        <img src="/img/loading.gif" style="display:none" id="actionStatusUP" />                    
        <apex:pageBlockButtons location="bottom" >                                                                                                          
        <!-- Save Button to insert the records -->
            <apex:commandButton value="Save" action="{!save}" rendered="{! reVariableSave}" onclick="document.getElementById('imageSV').style.display = 'inline';" />
            <img src="/img/loading.gif" style="display:none" id="imageSV" />
        </apex:pageBlockButtons>
        <p style="height:13px; font-size:13px"><b><br/> 
            Please be sure to upload a .csv file. You can find an example for the file type 
            <apex:commandLink action="https://storecapital--sandboxa--c.sandbox.vf.force.com/resource/1669504995000/PitchbookTestFile?" value="here"/></b>
        </p>
        <br/>
    </apex:pageBlock>

    <apex:pageBlock rendered="{! reVariableBlock}" id="idTable">
        <apex:pageBlockSection collapsible="false" columns="2" >
            <p><b>Total Records in CSV File:&nbsp;</b></p>
            <apex:outputText value="{! totalRecords}" style="color:black" />
            <p><b>Number of Records Successfully inserted:&nbsp;</b></p>
            <apex:outputText value="{! insertedRecords}" style="color:green" />
            <p><b>Number of Failed Records:&nbsp;</b></p>
            <apex:outputText value="{! failedRecords}" style="color:red" />
        </apex:pageBlockSection><br/>
        <center><p style="color:dodgerblue;font-size:25px"><b>Details of the inserted records</b></p></center><br/><br/>
        <apex:pageBlockTable value="{! leadsList}" rendered="{! reVariable}" var="lds" >                                                           
        <!-- Table to display details of inserted records -->
            <apex:repeat value="{! fieldNamesList}" var="fld" >
                <apex:column value="{! lds[fld]}" />
            </apex:repeat>
        </apex:pageBlockTable>
    </apex:pageBlock>
    
</apex:form>
</apex:page>

Controller:

public with sharing class UploadCSVController {

//Public Variables----------------------------------------------------------------------------------------------------------------------------------------------
public transient Blob    fileBody{ get; set; }                              //fileBody
public transient Integer fileSize{ get; set; }                              //fileSize
public transient String  fileName{ get; set; }                              //fileName
public List<Lead>        leadsList{ get; set; }                             //List of inserted Leads
public List<String>      fieldNamesList{ get; set; }                        //List of fields in Lead Object's fields which are avaiable in CSV
public Boolean           reVariableSave{ get; set; }                        //Variable to render Save Button
public Boolean           reVariableBlock{ get; set; }                       //Variable to render PageBlock with inserted record details
public Boolean           reVariable{ get; set; }                            //Variable to render Record Details Table    
public Integer           totalRecords{ get; set; }                          //Total number of records in CSV File
public Integer           insertedRecords{ get; set; }                       //Number of records successfully inserted
public Integer           failedRecords{ get; set; }                         //Number of failed records

//Private Variables----------------------------------------------------------------------------------------------------------------------------------------------
String fileBodyAsString = '';                                               
//String value of file Body
String header           = '';

//Constructor----------------------------------------------------------------------------------------------------------------------------------------------------
public UploadCSVController(){
    leadsList           = new List<SObject>();
    fieldNamesList      = new List<String>();
    reVariableSave      = false;
    reVariableBlock     = false;
    reVariable          = false;
    totalRecords        = 0;
    insertedRecords     = 0;
    failedRecords       = 0;    
}

//Method to check file size and whether the file body is readable------------------------------------------------------------------------------------------------
public void ReadFromFile(){
    reVariableBlock = false;
    if(fileSize < 3280760 && fileName.substringAfterLast('.').equalsIgnoreCase('csv')){
        system.debug('file size' + filesize);
        system.debug('file name after' + fileName.substringAfterLast('.'));
        system.debug('fileBodyAsString ' + fileBodyAsString);
        system.debug('fileBody.toString() ' + fileBody.toString());
        try{
            fileBodyAsString = fileBody.toString();
            ReadCSVFile();
        }
        catch(exception e){
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,'Error reading CSV file'));
        }
    }
    else{
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,'No File Chosen or,'));
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,'File Size greater than 50 KB or,'));
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,'File is not of CSV type'));
    }
}

//Method to read the file and create a Lead list which will be inserted and check exceptions in CSV file------------------------------------------------------
private void ReadCSVFile(){
    if(fileBodyAsString.length() > 100000){
        header = fileBodyAsString.substring(0, 2000).split('\n')[0];
        system.debug('line 67 passed');
    }
    else{
        header = fileBodyAsString.split('\n')[0];
        system.debug('line 71 passed');
    }
    fileBodyAsString = fileBodyAsString.substringAfter('\n');
    system.debug('field Name List before clear ' + fieldNamesList);
    leadsList.clear();
    fieldNamesList.clear();
    system.debug('line 78 passed');
    for(String str : header.split('\n')[0].split(',')){
        fieldNamesList.add(str.trim());
    }
    system.debug('line 81 passed');
    system.debug('fieldNamesList line 81 ' + fieldNamesList);
    String                      LeadDetails         = '';
    Map<string, SObjectField>   fieldNamesMap       = Schema.getGlobalDescribe().get('Lead').getDescribe().fields.getMap();
    System.debug('Field Name List After Clear before if check ' + fieldNamesList);
    System.debug('Field Name List After Clear before if check ' + fieldNamesList[0]);
    system.debug('line 84 passed');
    System.debug('fieldNamesMap ' + fieldNamesMap);
    System.debug('LeadDetails ' + LeadDetails);
    if(fieldNamesList[0].equalsIgnoreCase('LastName')){
        System.debug('Line 91 passed');
        Lead lds                = new Lead();
        Integer flag            = 0; 
        while( !String.isEmpty(fileBodyAsString)){                                                                 
            
            //Itereation over each Lead
            if(fileBodyAsString.length() > 100000){
                leadDetails = fileBodyAsString.substring(0, 100000).split('\n')[0];
            }
            else{
                leadDetails = fileBodyAsString.split('\n')[0];
            }
            fileBodyAsString = fileBodyAsString.substringAfter('\n');
            String lastnameValue = leadDetails.substringBefore(',').trim();
            for(Integer j=0; j<fieldNamesList.size(); j++){                                                                 
                //Iterating over the fields & assigning value to them for each Lead 
                Schema.DisplayType fieldType = fieldNamesMap.get(fieldNamesList[j]).getDescribe().getType();
                if( fieldType == Schema.DisplayType.DATE ){              
                    //Setting value of fields which are of Date Type
                    try{
                        lds.put(fieldNamesList[j].trim(), Date.valueOf(leadDetails.substringBefore(',').trim()));
                    }
                    catch(Exception e){
                        flag = 1;
                        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, 'Empty ' 
                                                                   + fieldNamesList[j].trim() 
                                                                   + ' field or Date is not in format \"YYYY-MM-DD\" for record with LastName = ' 
                                                                   + lastnameValue));
                    }
                }
                else if( fieldType == Schema.DisplayType.DATETIME ){ //Setting value of fields which are of DateTime Type
                    try{
                        lds.put(fieldNamesList[j].trim(), Datetime.valueOf(leadDetails.substringBefore(',').trim()));
                    }
                    catch(Exception e){
                        flag = 1;
                        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, 'Empty ' + fieldNamesList[j].trim() 
                                                                   + ' field or DateTime is not in format \"YYYY-MM-DD HH:MM:SS\" for record with LastName = ' 
                                                                   + lastnameValue));
                    }
                }
                else if( fieldType == Schema.DisplayType.BOOLEAN ){  //Setting value of fields which are of Boolean Type
                    if(leadDetails.substringBefore(',').trim().equalsIgnoreCase('true') 
                       || leadDetails.substringBefore(',').trim().equalsIgnoreCase('false') 
                       || leadDetails.substringBefore(',').trim() == ''){
                        lds.put(fieldNamesList[j].trim(), Boolean.valueOf(leadDetails.substringBefore(',').trim()));
                    }
                    else{
                        flag = 1;
                        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,  'Acceptable value for ' 
                                                                   + fieldNamesList[j].trim() 
                                                                   + ' field is \"TRUE/FALSE\" for record with LastName = ' 
                                                                   + lastnameValue));
                    }
                }
                else if( fieldType == Schema.DisplayType.TEXTAREA ){ //Setting value of fields which are of TextArea Type
                    if(leadDetails.left(1) != '\"'){                                                                 
                        //Setting value of fields which are of TextArea Type with comma
                        lds.put(fieldNamesList[j].trim(), leadDetails.substringBefore(',').trim());
                    }
                    else{                                                                                               
                        //Setting value of fields which are of TextArea Type without comma
                        lds.put(fieldNamesList[j].trim(), leadDetails.substringBetween('\"', '\"') .trim());
                        leadDetails = leadDetails.substringAfter('\"').substringAfter('\"');
                    }
                }
                else{                                                                                                   
                    //Setting value of all other type of fields
                    try{
                        lds.put(fieldNamesList[j].trim(), leadDetails.substringBefore(',').trim());
                    }
                    catch(Exception e){
                        flag = 1;
                    }
                }
                leadDetails = leadDetails.substringAfter(',');
            }
            leadsList.add(lds);
            lds = new Lead();
        }                  
        if(flag != 1){                                                                                                  
            //If there is no exception, show Save button
            reVariableSave = true;
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.INFO,  'Click Save Button to insert the Records '));
        }
    }
    else{
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,  'This has failed to work .... shit'));
    }
}

//Save method to insert the Lead Recods and counting inserted records and failed records----------------------------------------------------------------------
public Pagereference save(){
    reVariableBlock = true;
    Database.SaveResult[] srList = Database.insert(leadsList, false);
    leadsList.clear();
    Set<Id> savedLeadIdSet = new Set<Id>();
    totalRecords    = 0;
    insertedRecords = 0;
    failedRecords   = 0;
    for (Database.SaveResult sr : srList) {
        ++totalRecords;
        if (!sr.isSuccess()) {
            ++failedRecords;               
            for(Database.Error err : sr.getErrors()) {
                ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,  err.getStatusCode() 
                                                           + ': ' + err.getMessage() 
                                                           + ' for Record at Line Number: ' 
                                                           + (totalRecords + 1)));
            }
        }
        else{
            ++insertedRecords;
            savedLeadIdSet.add(sr.getId());
        }
    }
    leadsList = Database.query('SELECT ' + header + ' FROM Lead WHERE Id in :savedLeadIdSet');
    if(leadsList.size() > 0 && leadsList.size()<400){
        reVariable = true;
    }
    return null;
}
}

Test Class:

@isTest 
public class attachQuoteTestClass {      

static testmethod void testfileupload(){
    String body = 'LastName,firstName,Title,Company\n Testerson, Test, CEO, Rule27\n Testing, Tester, CIO, Rule27';
    String OUTPUT_DOCUMENT_NAME = 'Test File';
    insert new ContentVersion(
        Title = OUTPUT_DOCUMENT_NAME, 
        PathOnClient = OUTPUT_DOCUMENT_NAME + '.csv', 
        VersionData = Blob.valueOf(body), 
        ContentLocation = 'S'
    );
    UploadCSVController.ReadFromFile();
} 

static testmethod void testfileuploadNegative(){
    
}
}