Add DownloadError Tests

.github/minimum_coverage.txt

@@ -1 +1 @@
-0
+8

Tests/RogersBankDownloaderTests/DownloadErrorTests.swift

@@ -0,0 +1,31 @@
+@testable import RogersBankDownloader
+import XCTest
+
+final class DownloadErrorTests: XCTestCase {
+
+    func testDownloadErrorString() {
+        XCTAssertEqual(
+            "\(DownloadError.invalidJson(error: "ABC").localizedDescription)",
+            "The server response contained invalid JSON: ABC"
+        )
+        XCTAssertEqual(
+            "\(DownloadError.invalidParameters(parameters: ["a": "b", "c": "d"]).localizedDescription)",
+            """
+            The give parameters could not be converted to JSON: ["c": "d", "a": "b"]
+            """
+        )
+         XCTAssertEqual(
+            "\(DownloadError.httpError(error: "failed").localizedDescription)",
+            "An HTTP error occurred: failed"
+        )
+         XCTAssertEqual(
+            "\(DownloadError.noDataReceived.localizedDescription)",
+            "No data was received from the server"
+        )
+         XCTAssertEqual(
+            "\(DownloadError.invalidStatementNumber(-1).localizedDescription)",
+            "-1 is not a valid statement number to download"
+        )
+    }
+
+}