Add whitespace trimming test with copyright symbol (#147)

Resolve #141.

* Example of wrong whitespace trimming when copyright symbol is present
* Set decoder.trimValueWhitespaces to false in test
* Move repeated string to constant

Tests/XMLCoderTests/SpacePreserveTest.swift

@@ -16,12 +16,26 @@ private let nestedXML = """
 <si><t xml:space="preserve"> </t></si>
 """.data(using: .utf8)!
 
+private let copyright = "Copyright © 2019 Company, Inc."
+
+private let copyrightXML = """
+<t>\(copyright)</t>
+""".data(using: .utf8)!
+
+private let nestedCopyrightXML = """
+<si><t>\(copyright)</t></si>
+""".data(using: .utf8)!
+
 private struct Item: Codable, Equatable {
     public let text: String?
 
     enum CodingKeys: String, CodingKey {
         case text = "t"
     }
+
+    init(text: String?) {
+        self.text = text
+    }
 }
 
 final class SpacePreserveTest: XCTestCase {
@@ -51,4 +65,14 @@ final class SpacePreserveTest: XCTestCase {
         ).decode(Item.self, from: nestedXML)
         XCTAssertFalse(item.text?.isEmpty ?? true)
     }
+
+    func testCopyright() throws {
+        let decoder = XMLDecoder()
+        decoder.trimValueWhitespaces = false
+        let result = try decoder.decode(String.self, from: copyrightXML)
+        XCTAssertEqual(result, copyright)
+
+        let item = try decoder.decode(Item.self, from: nestedCopyrightXML)
+        XCTAssertEqual(item, Item(text: copyright))
+    }
 }