Salesforce APEX Unit Test Error with REST Services / Error at SELECT of Case Object - unit-testing

Question

I've succeeded to successfully construct a REST API using APEX language defined with an annotation: #RestResource.
I also wrote a matching Unit test procedure with #isTest annotation. The execution of the REST API triggered by a HTTP GET with two input parameters works well, while the Unit Test execution, returns a "null" value list resulting from the SOQL query shown below:
String mycase = inputs_case_number; // for ex. '00001026'
sObject[] sl2 = [SELECT Id, CaseNumber FROM Case WHERE CaseNumber = :mycase LIMIT 1];
The query returns:
VARIABLE_ASSIGNMENT [22]|sl2|[]|0x1ffefea6
I've also tried to execute it with a RunAs() method (see code below), using a dynamically created Salesforce test user, not anonymous, connected to a more powerful profile, but still receiving a "null" answer at the SOQL query. The new profile defines "View All" permission for Cases. Other SOQL queries to objects like: "User" and "UserRecordAccess" with very similar construction are working fine, both for REST APEX and Test APEX.
Is there a way to configure an access permission for Unit test (#isTest) to read the Case object and a few fields like: Id and CaseNumber. Is this error related to the "Tooling API" function and how can we fix this issue in the test procedure?
Code attachment: Unit Test Code
#isTest
private class MyRestResource1Test {
static testMethod void MyRestRequest() {
// generate temporary test user object and assign to running process
String uniqueUserName = 'standarduser' + DateTime.now().getTime() + '#testorg.com';
Profile p = [SELECT Id FROM Profile WHERE Name='StandardTestUser'];
User pu = new User(Alias='standt',Email='standarduser#testorg.com',LastName='testing',EmailEncodingKey='UTF-8',LanguageLocaleKey='en_US',LocaleSidKey='en_US',ProfileId=p.Id,TimeZoneSidKey='America/New_York',UserName=uniqueUserName);
System.RunAs(pu) {
RestRequest req = new RestRequest();
RestResponse res = new RestResponse();
req.requestURI = '/services/apexrest/sfcheckap/';
req.addParameter('useremail','testuserid#red.com');
req.addParameter('casenumber','00001026');
req.httpMethod = 'GET';
RestContext.request = req;
RestContext.response = res;
System.debug('Current User assigned is: ' + UserInfo.getUserName());
System.debug('Current Profile assigned is: ' + UserInfo.getProfileId());
Test.startTest();
Map<String, Boolean> resultMap = MyRestResource1.doGet();
Test.stopTest();
Boolean debugflag = resultMap.get('accessPermission');
String debugflagstr = String.valueOf(debugflag);
System.assert(debugflagstr.contains('true'));
}
}
}

Answer 1

Found a solution path by using: #isTest(SeeAllData=true)
See article: "Using the isTest(SeeAllData=true) Annotation"
https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_testing_seealldata_using.htm