WIP

tests/clipboredtests/DiagnosticsServiceTests.swift

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+import XCTest
+@testable import ClipBored
+
+final class DiagnosticsServiceTests: XCTestCase {
+  func testCountersCanBeIncrementedAndReset() {
+    let diagnostics = DiagnosticsService.shared
+    diagnostics.reset()
+
+    diagnostics.incrementMonitorTick()
+    diagnostics.incrementPasteboardChange()
+    diagnostics.incrementExtractionAttempt()
+    diagnostics.incrementDatabaseMutation()
+    diagnostics.incrementCachePurge()
+
+    // The counters use a serial async queue for low overhead; sync through reset's queue by reading a snapshot.
+    let snapshot = waitForSnapshot { diagnostics.currentSnapshot() }
+    XCTAssertEqual(snapshot.monitorTicks, 1)
+    XCTAssertEqual(snapshot.pasteboardChanges, 1)
+    XCTAssertEqual(snapshot.extractionAttempts, 1)
+    XCTAssertEqual(snapshot.databaseMutations, 1)
+    XCTAssertEqual(snapshot.cachePurges, 1)
+
+    diagnostics.reset()
+    XCTAssertEqual(diagnostics.currentSnapshot(), .init(monitorTicks: 0, pasteboardChanges: 0, extractionAttempts: 0, databaseMutations: 0, cachePurges: 0))
+  }
+
+  private func waitForSnapshot(_ snapshot: @escaping () -> DiagnosticsService.Snapshot) -> DiagnosticsService.Snapshot {
+    let expectation = expectation(description: "diagnostics queue")
+    DispatchQueue.global().asyncAfter(deadline: .now() + 0.05) {
+      expectation.fulfill()
+    }
+    wait(for: [expectation], timeout: 1)
+    return snapshot()
+  }
+}