Added test for server operation mode.

Tests/Segment-Tests/Analytics_Tests.swift

@@ -644,4 +644,38 @@ final class Analytics_Tests: XCTestCase {
         XCTAssertTrue(shared2 === shared)
 
     }
+
+    func testServerOperatingMode() {
+        // Use a specific writekey to this test so we do not collide with other cached items.
+        let analytics = Analytics(configuration: Configuration(writeKey: "testFlush_serverMode")
+            .flushInterval(9999)
+            .flushAt(9999)
+            .operatingMode(.server))
+
+        waitUntilStarted(analytics: analytics)
+
+        analytics.storage.hardReset(doYouKnowHowToUseThis: true)
+
+        @Atomic var completionCalled = false
+
+        // put an event in the pipe ...
+        analytics.track(name: "completion test1")
+        // flush it, that'll get us an upload going
+        analytics.flush {
+            // verify completion is called.
+            completionCalled = true
+        }
+
+        // completion shouldn't be called before flush returned.
+        XCTAssertTrue(completionCalled)
+        XCTAssertEqual(analytics.pendingUploads!.count, 0)
+
+        // put another event in the pipe.
+        analytics.track(name: "completion test2")
+        analytics.flush()
+
+        // flush shouldn't return until all uploads are done, cuz
+        // it's running in sync mode.
+        XCTAssertEqual(analytics.pendingUploads!.count, 0)
+    }
 }