public class Calculator {
 public class CalculatorException extends Exception{}

  public static Integer addition(Integer a, Integer b){
   return a + b;
    }

   public static Integer subtraction(Integer a, Integer b){
    return a - b;
    }

 public static Integer multiply(Integer a, Integer b){
  if(b==0 || a==0){
  throw new CalculatorException('It doesn\'t make sense to multiply by 
   zero');
  }
  return a * b;
  }

 public static Decimal divide(Integer numerator, Integer denominator){
  if(denominator == 0){
  throw new CalculatorException('you still can\'t divide by zero');
   }
 Decimal returnValue = numerator / denominator;
  if(returnValue < 0){
    throw new CalculatorException('Division returned a negative value.' + 
 returnValue);
 }
   return returnValue;
  }


 }

@isTest
   public class Calculator_Tests {

@isTest
 public static void addition() {
    Calculator.addition(1, 0);
   }
@isTest
  public static void subtraction() {
    Calculator.subtraction(1, 0);
   }

@isTest
 public static void divide_throws_exception_for_division_by_zero() {
 Boolean caught = false;
 try {
    Calculator.divide(1, 0);
  } catch (Calculator.CalculatorException e) {
    System.assertEquals('you still can\'t divide by zero', e.getMessage(), 
  'caught the right exception');
    caught = true;
   }
   System.assert(caught, 'threw expected exception');
   }

  @isTest
 public static void divide_throws_exception_for_division_by_two() {
 Boolean caught = true;
 try {
    Calculator.divide(1, 2);
 } catch (Calculator.CalculatorException e) {
    System.assertEquals('you still can\'t divide by zero', e.getMessage(), 
  'caught the right exception');
    caught = true;
   }
   System.assert(caught, 'threw expected exception');
 }


@isTest
public static void multiply_by_one() {
  Boolean caught = false;
  try {
    Calculator.multiply(1, 0);
    } catch (Calculator.CalculatorException e) {
    System.assertEquals('It doesn\'t make sense to multiply by zero', 
    e.getMessage(), 'caught the right exception');
     caught = true;
    }
    System.assert(caught, 'threw expected exception');
  }

@isTest
 public static void multiply_by_two() {
  Boolean caught = true;
  try {
     Calculator.multiply(1, 2);
   } catch (Calculator.CalculatorException e) {
    System.assertEquals('It doesn\'t make sense to multiply by zero', 
  e.getMessage(), 'caught the right exception');
    caught = true;
   }
   System.assert(caught, 'threw expected exception');
}   
}

public class UpdateContactPageLayout {
    // Add custom field to page layout
    
    public Metadata.Layout addLayoutItem () {
        
        // Retrieve Contact layout and section 
        List<Metadata.Metadata> layoutsList = 
            Metadata.Operations.retrieve(Metadata.MetadataType.Layout, 
            new List<String> {'Contact-Contact Layout'});
        Metadata.Layout layoutMetadata = (Metadata.Layout) layoutsList.get(0);
        Metadata.LayoutSection contactLayoutSection = null;
        List<Metadata.LayoutSection> layoutSections = layoutMetadata.layoutSections;
        for (Metadata.LayoutSection section : layoutSections) {
            
            if (System.equals(section.label, 'Additional Information')) {
                contactLayoutSection = section;
                break;
            }
        }
        
        // Add the field under Contact info section in the left column
        List<Metadata.LayoutColumn> contactColumns = contactLayoutSection.layoutColumns;     
        List<Metadata.LayoutItem> contactLayoutItems = contactColumns.get(0).layoutItems;
        
        // Create a new layout item for the custom field
        Metadata.LayoutItem newField = new Metadata.LayoutItem();
        newField.behavior = Metadata.UiBehavior.Edit;
        newField.field = 'BOBN_TRAILHEAD__Apex_MD_API_Twitter_name__c';
        contactLayoutItems.add(newField);
        
        return layoutMetadata;
    }
}

• Create an Apex class called CaseService that contains a void static method called closeCases that takes a set of Case IDs and a String parameter for the close reason.
• Create a REST Apex class called CaseCloseResource with a URL mapping /case/*/close (where * will be the Id). Implement a POST closeCase method which accepts a String reason and calls the CaseService.closeCases service method passing in the Id and close reason.

global with sharing class CaseService {

    global static void closeCases(List<Id> caseIds, String closingReason) {
        if (caseIds == null || caseIds.size() == 0) {
            throw new CaseServiceException('You should tell me which cases you wanna close');
        }
        
        if (closingReason == null || closingReason == '') {
            throw new CaseServiceException('I won\'t close a case without any reason');
        }
        
        List<Case> closedCases = new List<Case>();
        
        for(Id caseId : caseIds) {
            Case caseToClose = new Case(
            	Id = caseId,
                Status = 'Closed',
                Reason = closingReason
            );
            closedCases.add(caseToClose);
        }
        
        SavePoint sp = Database.setSavepoint();
        if (closedCases.size() > 0) {
            try {
                update closedCases;
            } catch (Exception e) {
                Database.rollback(sp);
                throw e;
            }
        }
    }
    
    public class CaseServiceException extends Exception {}
}

@RestResource(urlMapping='/case/*/close')
global with sharing class CaseCloseResource {
    
    @HttpPost
    global static void closeCase(String reason) {                
        Id id = RestContext.request.requestURI.substringBetween('case/', '/close');
        CaseService.closeCases(new Id[]{id}, reason);
    }
}

Id id = '5000Y000002Vc8Y';
CaseService.closeCases(new Id[]{id}, 'You shall be closed!');

POST /services/apexrest/case/5000Y000002Vc8m/close
Payload : {"reason" : "Please close this case too!"}

<aura:component controller="CampingListController">
    
    <aura:handler name="init" action="{!c.doInit}" value="{!this}"/>
    <aura:handler name="addItem" event="c:addItemEvent" action="{!c.handleAddItem}"/>
    
    <div class="slds-page-header" role="banner">

      <div class="slds-grid">

        <div class="slds-col">

          <p class="slds-text-heading--label">Camping Items</p>

          <h1 class="slds-text-heading--medium">My Camping Items</h1>

        </div>

      </div>

    </div>

      
  <div aria-labelledby="newitemform">

      <fieldset class="slds-box slds-theme--default slds-container--small">
    
        <c:campingListForm />
    
      </fieldset>

	</div>
    
    
     <aura:attribute name="items" type="Camping_Item__c[]"/>

    <div class="slds-card slds-p-top--medium">
        <header class="slds-card__header">
            <h3 class="slds-text-heading--small">Camping List Items</h3>
        </header>
        
        <section class="slds-card__body">
            <div id="list" class="row">
                <aura:iteration items="{!v.items}" var="campItem">
                    <c:campingListItem item="{!campItem}"/>
                </aura:iteration>
            </div>
        </section>
    </div>

</aura:component>

({
    
    doInit: function(component, event, helper) {
    
        var action = component.get("c.getItems");
    
        action.setCallback(this, function(response) {
            var state = response.getState();
            if (component.isValid() && state === "SUCCESS") {
                component.set("v.items", response.getReturnValue());
            }
            else {
                console.log("Failed with state: " + state);
            }
        });
    
        $A.enqueueAction(action);
    },    
    
    handleAddItem: function(component, event, helper) {
        var item = event.getParam("item");
                
        var action = component.get("c.saveItem");
        action.setParams({
            "item": item
        });
        
        action.setCallback(this, function(response){
            var state = response.getState();
            if (component.isValid() && state === "SUCCESS") {        
                var theItems = component.get("v.items");
                theItems.push(item);
                component.set("v.items",theItems);
            }
        });
        $A.enqueueAction(action);
    }
    
})

public with sharing class CampingListController {

    @AuraEnabled 
    public static List<Camping_Item__c> getItems() {
        return [SELECT Id, Name, Price__c, Quantity__c, Packed__c FROM Camping_Item__c];
    }
    
    @AuraEnabled
    public static Camping_Item__c saveItem(Camping_Item__c item) {
        upsert item;
        return item;
    }
}

<aura:component >
    
     <aura:attribute name="newItem" type="Camping_Item__c"
     default="{ 'sobjectType': 'Camping_Item__c',
                    'Name': '',
                    'Packed__c': false,
                    'Price__c': '0',
                    'Quantity__c': '0' }"/>
	<aura:registerEvent name="addItem" type="c:addItemEvent"/>
    
  <div aria-labelledby="newitemform">
      <fieldset class="slds-box slds-theme--default slds-container--small">
    
        <legend id="newitemform" class="slds-text-heading--small 
          slds-p-vertical--medium">
          Add Camping Item
        </legend>
    
        <form class="slds-form--stacked">
    
          <div class="slds-form-element slds-is-required">
              <div class="slds-form-element__control">
                  <ui:inputText aura:id="name" label="Camping Item Name"
                      class="slds-input"
                      labelClass="slds-form-element__label"
                      value="{!v.newItem.Name}"
                      required="true"/>
              </div>
         </div>
            
          <div class="slds-form-element">
              <ui:inputCheckbox aura:id="packed" label="Packed?"
                  class="slds-checkbox"
                  labelClass="slds-form-element__label"
                  value="{!v.newItem.Packed__c}"/>
          </div>
            
        <div class="slds-form-element">
              <div class="slds-form-element__control">
                  <ui:inputCurrency aura:id="price" label="Price"
                      class="slds-input"
                      labelClass="slds-form-element__label"
                      value="{!v.newItem.Price__c}" />
    
              </div>
          </div>
    
         <div class="slds-form-element">
              <div class="slds-form-element__control">
                  <ui:inputNumber aura:id="quantity" label="Quantity"
                      class="slds-input"
                      labelClass="slds-form-element__label"
                      value="{!v.newItem.Quantity__c}"/>
    
              </div>
          </div>
    
          <div class="slds-form-element">
              <ui:button label="Create Camping Item"
                  class="slds-button slds-button--brand"
                  press="{!c.clickCreateCampingItem}"/>
          </div>
    
        </form>
    
      </fieldset>
</div>

</aura:component>

({    
    
    clickCreateCampingItem : function(component, event, helper) {
        
        var validCamping = true;

        // Name must not be blank
        var nameField = component.find("name");
        var expname = nameField.get("v.value");
        if ($A.util.isEmpty(expname)){
            validCamping = false;
            nameField.set("v.errors", [{message:"Camping Item name can't be blank."}]);
        }
        else {
            nameField.set("v.errors", null);
        }

        
        var priceField = component.find("price");
        var price = priceField.get("v.value");
        if ($A.util.isEmpty(price) || isNaN(price) || (price <= 0.0)){
            validCamping = false;
            priceField.set("v.errors", [{message:"Camping Item price can't be blank."}]);
        }
        else {
            priceField.set("v.errors", null);
        }
        
        var quantityField = component.find("quantity");
        var quantity = quantityField.get("v.value");
        if ($A.util.isEmpty(quantity) || isNaN(quantity) || (quantity <= 0)){
            validCamping = false;
            quantityField.set("v.errors", [{message:"Camping Item quantity can't be blank."}]);
        }
        else {
            quantityField.set("v.errors", null);
        }

        if(validCamping){
            
            helper.createItem(component);
            
        }
        
    },
})

({
    
     createItem : function(component) {
        var newItem = component.get("v.newItem");
        var addEvent = component.getEvent("addItem");
        addEvent.setParams({"item" : newItem});
        addEvent.fire();
        component.set("v.newItem",
                     { 'sobjectType': 'Camping_Item__c',
                    'Name': '',
                    'Packed__c': false,
                    'Price__c': 0,
                    'Quantity__c': 0});
    }
})

public class AccountProcessor {
     @future

  public static void someFutureMethod(List<id> scope) {

   Account[] updates = new Account[] {};
        for (AggregateResult ar : [
                select AccountId a, count(Id) c
                from Contact
                where AccountId in :scope
                group by AccountId
                ]) {
            updates.add(new Account(
                    Id = (Id) ar.get('a'),
                    Number_of_Contacts__c = (Decimal) ar.get('c')
                    ));
        }
        update updates;
    }

}

@IsTest
public class AccountProcessorTest {
  public static testmethod void TestAccountProcessorTest() {
 
Test.startTest();
     Account a = new Account();
        a.Name = 'Test Account';
        Insert a;
      
      Contact cont = New Contact();
      
      cont.FirstName ='Bob';
      cont.LastName ='Masters';
      cont.AccountId = a.Id;
      Insert cont;

    Test.stopTest() ;
     Contact ACC = [select AccountId from Contact where id = :a.id LIMIT 1];

 
        System.assert(Cont.AccountId != null);
        System.assertequals(cont.id, ACC.AccountId);

  }}

I have created HelloWorld example class in developer console which is in apex work book

public class UpdateContactPageLayout {
    // Add custom field to page layout
    
    public Metadata.Layout addLayoutItem () {
        
        // Retrieve Contact layout and section 
        List<Metadata.Metadata> layoutsList = 
            Metadata.Operations.retrieve(Metadata.MetadataType.Layout, 
            new List<String> {'Contact-Contact Layout'});
        Metadata.Layout layoutMetadata = (Metadata.Layout) layoutsList.get(0);
        Metadata.LayoutSection contactLayoutSection = null;
        List<Metadata.LayoutSection> layoutSections = layoutMetadata.layoutSections;
        for (Metadata.LayoutSection section : layoutSections) {
            
            if (System.equals(section.label, 'Additional Information')) {
                contactLayoutSection = section;
                break;
            }
        }
        
        // Add the field under Contact info section in the left column
        List<Metadata.LayoutColumn> contactColumns = contactLayoutSection.layoutColumns;     
        List<Metadata.LayoutItem> contactLayoutItems = contactColumns.get(0).layoutItems;
        
        // Create a new layout item for the custom field
        Metadata.LayoutItem newField = new Metadata.LayoutItem();
        newField.behavior = Metadata.UiBehavior.Edit;
        newField.field = 'BOBN_TRAILHEAD__Apex_MD_API_Twitter_name__c';
        contactLayoutItems.add(newField);
        
        return layoutMetadata;
    }
}