String FirstName = UserInfo.getFirstName();//Returns the context user's first name.
System.Debug('FirstName-' + FirstName);
String LastName = UserInfo.getLastName();//Returns the context user's last name.
System.Debug('LastName-' + LastName);
String Name = UserInfo.getName();//Returns the context user's full name.
System.Debug('Name-' + Name);
String UserEmail = UserInfo.getUserEmail();//Returns the current user’s email address.
System.Debug('UserEmail-' + UserEmail);
String UserType = UserInfo.getUserType();//Returns the context user's type.
System.Debug('UserType-' + UserType);
String UserId = UserInfo.getUserId();//Returns the context user's ID.
System.Debug('UserId-' + UserId);
String UserName = UserInfo.getUserName();//Returns the context user's login name.
System.Debug('UserName-' + UserName);
String ProfileId = UserInfo.getProfileId();//Returns the context user's profile ID.
System.Debug('ProfileId-' + ProfileId);
String UserRoleId = UserInfo.getUserRoleId();//Returns the context user's role ID.
System.Debug('UserRoleId-' + UserRoleId);
String SessionId = UserInfo.getSessionId();//Returns the session ID for the current session.
System.Debug('SessionId-' + SessionId);
TimeZone tz = UserInfo.getTimeZone();//Returns the current user’s local time zone.
System.Debug('TimeZone-' + tz);
String DefaultCurrency = UserInfo.getDefaultCurrency();//Returns the context user's default currency code for multiple currency organizations or the organization's currency code for single currency organizations.
System.Debug('DefaultCurrency-' + DefaultCurrency);
String Language = UserInfo.getLanguage();//Returns the context user's language.
System.Debug('Language-' + Language);
String Locale = UserInfo.getLocale();//Returns the context user's locale.
System.Debug('Locale-' + Locale);
String OrganizationId = UserInfo.getOrganizationId();//Returns the context organization's ID.
System.Debug('OrganizationId-' + OrganizationId);
String OrganizationName = UserInfo.getOrganizationName();//Returns the context organization's company name.
System.Debug('OrganizationName-' + OrganizationName);

For Custom Controller

//Page reference to your VF Page
PageReference pageRef = Page.TestPage;
Test.setCurrentPage(pageRef);

//Pass necessary parameter
pageRef.getParameters().put('Id',id); 

//init controller 
CustomCtrl objCtrl = new CustomCtrl();

//Call pageRef mymethod
PageReference objPageRef = objCtrl.mymethod();

//Put system asserts
System.assertEquals (null,pageRef);

For Standard Controller

//First create record
Account acc = New Account();
acc.Name = 'Test Account';
INSERT acc;

//Page reference to your VF Page
PageReference pageRef = Page.TestPage;
Test.setCurrentPage(pageRef);

//Pass necessary parameter
pageRef.getParameters().put('Id',acc.id);   

//Pass your object to controller     
ApexPages.StandardController stc = new ApexPages.StandardController(acc);

//Call controller
CustomCtrl objCtrl = new CustomCtrl(stc);

//Call pageRef mymethod
PageReference objPageRef = objCtrl.mymethod();

//Put system asserts
System.assertEquals (null,pageRef);

We can use apex:commandLink to redirect a visualforce page in a new Tab URL using PageReference in apex class.

Sample Code:

VF Page:

<apex:page controller="SampleleRedirect">
	<apex:form >
		<apex:pageblock >
			<apex:commandlink action="{!redirect}" target="_blank">
				<apex:commandButton value="Open in New Tab"/>
			</apex:commandLink>
		</apex:pageblock>
	</apex:form>
</apex:page> 

Apex Controller:

public class SampleleRedirect {   

	public SampleleRedirect() {
	
	}

	public pageReference redirect() {
		PageReference pageRef = new PageReference('http://www.biswajeetsamal.com');
		pageRef.setRedirect(true);
		return pageRef;
	}            
}