Clean up for loader tests

Remove or combine duplicate tests.
Remove commented out code.
Small changes to values used in some tests to more accurately reflect
usage.
Add helper function for use in tests that check that a resource is being
loaded correctly.
Change message about a loaded file not being FHIR json from info to
debug, since this event is normal.

src/loader/BasePackageLoader.ts

@@ -126,7 +126,7 @@ export class BasePackageLoader implements PackageLoader {
           this.loadResourceFromCache(resourcePath, packageName, packageVersion);
         } catch {
           // swallow this error because some JSON files will not be resources
-          this.log('info', `JSON file at path ${resourcePath} was not FHIR resource`);
+          this.log('debug', `JSON file at path ${resourcePath} was not FHIR resource`);
         }
       });
   }