Need Test Class for following scenario..Where VF Page display a form that take input and add record in Student object.
Please consider all positive negative test cases.

---------------------------------------------------VF Page----------------------------------------------------------
<apex:page standardController="Student__c" extensions="StudentRegFormExtension" language="{!selectedLang }"
    sidebar="false" 
>
    <apex:form >
        <apex:selectList value="{!selectedLang}" size="1">
            <apex:selectoptions value="{!listOfLang}"/>
            <apex:actionsupport event="onchange" reRender="form"/>
        </apex:selectlist>

        <apex:outputPanel id="pageMessage">
            <apex:pageMessages rendered="true" ></apex:pageMessages>
        </apex:outputPanel>

        <apex:pageblock >
                <apex:pageblocksection id="form">
                    <apex:inputfield value="{! Student__c.Name }"/>
                    <apex:inputfield value="{! Student__c.Roll_Number__c }"/>
                   
                    <apex:inputfield value="{! Student__c.Gender__c }"/>
                    <apex:inputfield value="{! Student__c.Course_Applying_For__c }"/>
                    <apex:inputfield value="{! Student__c.SSC__c }"/>
                    <apex:inputfield value="{! Student__c.HSC__c }"/>
                    <apex:inputfield value="{! Student__c.City__c }"/>
                    <apex:inputfield value="{! Student__c.State__c }"/>
                    <apex:inputfield value="{! Student__c.Country__c }"/>
                </apex:pageblocksection>
                <div align="center" draggable="false" >
                       <apex:commandButton value="{!$Label.Record_Inserted}" action="{! save}" reRender="pageMessage"/>
                       </div>
        </apex:pageblock>
    </apex:form>
</apex:page>

---------------------------------------------------CONTROLLER-------------------------------------------------------------
public class StudentRegFormExtension {
    
    public Boolean showMessage{get;set;}
    public String selectedLang{get;set;}
    public List<SelectOption> listOfLang {get;set;}
    public ApexPages.StandardController controller{get;set;}
  
    
    public StudentRegFormExtension(ApexPages.StandardController con) {
       controller = con;
       showMessage = false;
        listOfLang = new List<SelectOption>();
        listOfLang.add(new SelectOption('en','English'));
        listOfLang.add(new SelectOption('es','Spanish'));
        listOfLang.add(new SelectOption('fr','French'));
     if(ApexPages.currentPage().getParameters().get('Success') != null ) {
            ApexPages.addmessage(new ApexPages.message(ApexPages.severity.CONFIRM,
            System.Label.Record_Inserted));
       
    }
    }
    
     public PageReference save() {

        Student__c student = (Student__c)controller.getRecord();
        PageReference pr;
        if(student.Name == null) {
             ApexPages.addmessage(new ApexPages.message(ApexPages.severity.Error,
                System.Label.Error_Inserting_Record));

        }else {
            controller.save();
            pr = new PageReference('/apex/StudentRegForm?Success=true');
            pr.setRedirect(true);
        }
        return pr;
    }
}