What are the most common challenges faced while integrating salesforce with On-Prem Applications(SAP, Ivanti Heat, Sharepoint, Jenkins) vs cloud application(Sharepoint, Jenkins, Bitbucket, Microsoft TFS etc)?

I know there are multiple 3rd party applications and even direct API's available now, I want to know this with respect to creating own api's.
Request you to explain to me or provide a direction to extend me research

Hi,

I have an EmailMessage trigger (after insert), I'll do some checks of attachments (Notice my attachments are of ContentDocumentLink!)
The code looks like this following:

private static void doNotAllowProfilesSendEmailsWithAttachments(List<EmailMessage> newMessages) {

        if (!validateCurrentUserRule()) {
            System.debug('====User without the permission===');
            String digitalSignature = [SELECT CA_Digital_Signature__c FROM User WHERE Id = :UserInfo.getUserId()][0].CA_Digital_Signature__c;
            System.debug('===digitalSignature===='+digitalSignature);
            System.debug('===newMessages===='+newMessages);
            Set<String> msgIdSet = new Set<String>();
            Map<String, Set<String>> attMap = new Map<String, Set<String>>();
            for(EmailMessage msg:newMessages){
                msgIdSet.add(msg.Id);
            }
            System.debug('===msgIdSet===='+msgIdSet);
            for(ContentDocumentLink cdl :[SELECT Id, LinkedEntityId, ContentDocumentId, ContentDocument.title FROM ContentDocumentLink where LinkedEntityId IN :msgIdSet]){
                if(!attMap.containsKey(cdl.LinkedEntityId)){
                    attMap.put(cdl.LinkedEntityId, new Set<string>());
                }
                attMap.get(cdl.LinkedEntityId).add(cdl.ContentDocument.title);
            }
            System.debug('===attMap===='+attMap);
            for(EmailMessage msg:newMessages){
                if(msg.Incoming == FALSE){
                    for(String title : attMap.get(msg.Id)){
                        if(!digitalSignature.contains(title)){
                            msg.addError('You may not include an attachment in outbound emails.');
                            break;
                        }
                    }
                }
            }
        }
    }

And then my Unit test is:

@IsTest
    public static void doNotAllowProfilesSendEmailsWithAttachments_TestWrong() {

        String[]emails = new String[]{
                'wei.dong@pwc.com'
        };
        Boolean isSentSuccessful = true;

        // Test when we attach an attachment with 'Stand User'
        Profile p = [SELECT Id FROM Profile WHERE Name = 'Consumer Care Agent'];
        User u = new User(Alias = 'standt', Email = 'standarduser@testorg.com',
                EmailEncodingKey = 'UTF-8', LastName = 'Testing', LanguageLocaleKey = 'en_US',
                LocaleSidKey = 'en_US', ProfileId = p.Id,
                TimeZoneSidKey = 'America/Los_Angeles',
                UserName = 'standarduser_dongwei_test@testorg.com');

        Test.startTest();

        System.runAs(u) {

            // Insert a new contact for inner search contact ID
            Contact newContact = new Contact();
            newContact.LastName = 'Last Name';
            insert newContact;

            // 1. Create a Document as an attachment
            Document doc = new Document();
            doc.Name = 'Test document';
            doc.Body = Blob.valueOf('Test me');
            doc.ContentType = 'text/plain';
            doc.Type = 'txt';
            doc.FolderId = UserInfo.getUserId();
            insert doc;

            // 2. Preparing to attach the attachment
            Messaging.EmailFileAttachment file = new Messaging.EmailFileAttachment();
            file.setContentType('application/txt');
            file.setFileName('testAttachment.txt');
            // Make this as an attachment
            file.setInline(false);
            file.Body = doc.Body;


            // 3. Successfully sent
            Map<String, String> replacers = new Map<String, String>();
            replacers.put('dongwei', '');
            isSentSuccessful = CA_Utility.sendSingleEmail(emails,
                    'Test', 'Test body',replacers, 'DongWei',
                    true, new Messaging.EmailFileAttachment[]{
                            file
                    });
            System.assert(isSentSuccessful);

            EmailMessage email = new EmailMessage();
            email.FromAddress = 'test@abc.org';
            email.Incoming = True;
            email.ToAddress = 'test@xyz.org';
            email.Subject = 'Test email';
            email.HtmlBody = 'Test email body';

            Blob beforeblob = Blob.valueOf('Unit Test Attachment Body');

            ContentVersion cv = new ContentVersion();
            cv.title = 'Bad Signature Here';
            cv.PathOnClient = 'test';
            cv.VersionData = beforeblob;
            insert cv;

            ContentVersion testContent = [SELECT id, ContentDocumentId FROM ContentVersion where Id = :cv.Id];

            ContentDocumentLink contentlink = new ContentDocumentLink();
            contentlink.LinkedEntityId = email.Id;
            contentlink.ShareType = 'V';
            contentlink.ContentDocumentId = testcontent.ContentDocumentId;
            contentlink.LinkedEntityId = email.Id;

            email.ContentDocumentLinks.add(contentlink);
            insert email;
        }

        Test.stopTest();
    }

I tried to use Email attach to attach an attachments, but nothing hopes to improve the coverage; And when I tried to use "ContentDocumentLink" it still doesn't help. 

Any one can help me to improve the coverage about entering the 'for' of ContentDocumentLink in my trigger?

What are the most common challenges faced while integrating salesforce with On-Prem Applications(SAP, Ivanti Heat, Sharepoint, Jenkins) vs cloud application(Sharepoint, Jenkins, Bitbucket, Microsoft TFS etc)?

I know there are multiple 3rd party applications and even direct API's available now, I want to know this with respect to creating own api's.
Request you to explain to me or provide a direction to extend me research

Hi All,
Anybody out there who can help with API calls/integration requirement in my project. I am new to integration requirements so looking for help. Below is my requirement.
I have Opportunity object where i need to place a button 'SendRequest'. When user clicks on this button i need to validate some matching criteria. If criteria met then i need to send request with few fields info like opportunity type,stage, createddate to external system and update few fileds on opportunity upon receiving response.

Please help me to achieve this task.
Thanks In Advance.