feat: [add load function to EppoClient] (FF-2907) (#39)

* feat: [add `load` function to EppoClient] (FF-2907)

* typo in comment

Author: leoromanovsky

README.md

@@ -102,7 +102,6 @@ public class AssignmentObserver: ObservableObject {
 }
 ```
 
-
 Rendering the view:
 
 ```swift

Sources/eppo/EppoClient.swift

@@ -2,7 +2,7 @@ import Foundation;
 
 // todo: make this a build argument (FF-1944)
 public let sdkName = "ios"
-public let sdkVersion = "3.0.1"
+public let sdkVersion = "3.1.0"
 
 public enum Errors: Error {
     case notConfigured
@@ -99,6 +99,14 @@ public class EppoClient {
         }
         return instance
     }
+
+    // Loads the configuration from the remote source on-demand. Can be used to refresh as desired.
+    //
+    // This function can be called from multiple threads; synchronization is provided to safely update
+    // the configuration cache but each invocation will execute a new network request with billing impact.
+    public func load() async throws {
+        try await self.configurationStore.fetchAndStoreConfigurations()
+    }
 
     public static func resetSharedInstance() {
         sharedInstance = nil

Tests/eppo/SingletonTest.swift

@@ -47,6 +47,27 @@ final class EppoTests: XCTestCase {
         XCTAssertIdentical(eppoClient1, eppoClient2, "Changing host re-instantiates the singleton")
     }
 
+    func testLoadingMultithreading() async throws {
+        let expectedCount = 50
+        let expectation = XCTestExpectation(description: "eppo client expectation")
+        expectation.expectedFulfillmentCount = expectedCount
+        
+        Task {
+            await withThrowingTaskGroup(of: Void.self) { group in
+                for _ in 0 ..< expectedCount {
+                    group.addTask {
+                        _ = try await EppoClient.initialize(sdkKey: "mock-api-key")
+                        _ = try await EppoClient.shared().load()
+                        expectation.fulfill()
+                    }
+                }
+            }
+        }
+        
+        await fulfillment(of: [expectation], timeout: 5)
+        XCTAssertEqual(stubCallCount, 51) // initialize + 50 `load` executions
+    }
+    
     func testEppoClientMultithreading() async throws {
         let expectedCount = 50
         let expectation = XCTestExpectation(description: "eppo client expectation")