Added setExpirationDate implementation along with tests

spec/PKPass.ts

@@ -126,5 +126,42 @@ describe("PKPass", () => {
 
 			expect(pass.props["nfc"]).toBeUndefined();
 		});
+
+		describe("setExpirationDate", () => {
+			it("Won't apply changes without a valid argument", () => {
+				const pass = new PKPass({}, {});
+
+				// @ts-expect-error
+				pass.setExpirationDate();
+				expect(pass.props["expirationDate"]).toBe(undefined);
+
+				// @ts-expect-error
+				pass.setExpirationDate(42);
+				expect(pass.props["expirationDate"]).toBe(undefined);
+			});
+
+			it("expects a Date object as the only argument", () => {
+				const pass = new PKPass({}, {});
+
+				pass.setExpirationDate(new Date(2020, 6, 1, 0, 0, 0, 0));
+				// Month starts from 0 in Date Object when used this way, therefore
+				// we expect one month more
+				expect(pass.props["expirationDate"]).toBe(
+					"2020-07-01T00:00:00Z",
+				);
+			});
+
+			it("An invalid date, will not apply changes", () => {
+				const pass = new PKPass({}, {});
+
+				// @ts-expect-error
+				pass.setExpirationDate("32/18/228317");
+				expect(pass.props["expirationDate"]).toBe(undefined);
+
+				// @ts-expect-error
+				pass.setExpirationDate("32/18/228317");
+				expect(pass.props["expirationDate"]).toBe(undefined);
+			});
+		});
 	});
 });