Add a mock CKShare owned by current user (#18)

Canopy test tools previously provided a mock CKShare that was owned by another user, where current user was a regular participant.

This PR adds another mock share that is owned by the current user with two regular participants.

It also adds basic smoke tests to check that these shares are valid and can be unarchived successfully.

Targets/Canopy/Tests/MockObjectTests.swift

@@ -0,0 +1,19 @@
+@testable import Canopy
+import CanopyTestTools
+import CanopyTypes
+import CloudKit
+import Foundation
+import XCTest
+
+/// Test the validity mock objects provided as part of the test tools.
+final class MockObjectTests: XCTestCase {
+  func test_mock_share_owned_by_another_user() {
+    let share = CKShare.mock
+    XCTAssertEqual(share.participants.count, 2)
+  }
+
+  func test_mock_share_owned_by_current_user() {
+    let share = CKShare.mock_owned_by_current_user
+    XCTAssertEqual(share.participants.count, 3)
+  }
+}