Store and confirm what experiments a user is enrolled in

Sources/Experiments/ExPlat.swift

@@ -12,6 +12,7 @@ import Cocoa
 
     private let assignmentsKey = "ab-testing-assignments"
     private let ttlDateKey = "ab-testing-ttl-date"
+    private let enrolledKey = "ab-testing-enrolled-experiments"
 
     private(set) var experimentNames: [String] = []
 
@@ -23,6 +24,12 @@ import Cocoa
         return ttlDate.timeIntervalSinceReferenceDate - Date().timeIntervalSinceReferenceDate
     }
 
+    /// Check to see if ExPlat has stored the names of enrolled experiments
+    ///
+    public var enrolledArrayExists: Bool {
+        UserDefaults.standard.object(forKey: enrolledKey) != nil
+    }
+
     public init(configuration: ExPlatConfiguration,
                 service: ExPlatService? = nil) {
         self.service = service ?? ExPlatService(configuration: configuration)
@@ -81,6 +88,9 @@ import Cocoa
             ttlDate.addTimeInterval(TimeInterval(assignments.ttl))
             UserDefaults.standard.setValue(ttlDate, forKey: self.ttlDateKey)
 
+            let enrolledExperimentNames = assignments.variations.map({ $0.key })
+            UserDefaults.standard.setValue(enrolledExperimentNames, forKey: self.enrolledKey)
+
             completion?()
         }
     }
@@ -101,6 +111,17 @@ import Cocoa
         }
     }
 
+    /// Checks if the experiment name is contained in the enrolled experiments array
+    /// returns false if there is no dictionary or the experiment is not registered
+    ///
+    public func isEnrolled(in name: String) -> Bool {
+        guard let enrolled = UserDefaults.standard.object(forKey: enrolledKey) as? [String] else {
+            return false
+        }
+
+        return enrolled.contains(name)
+    }
+
     /// Check if the app is entering background and/or foreground
     /// and start/stop the timers
     ///