Add missingChatTemplate error (#199)

Author: DePasqualeOrg

Sources/Tokenizers/Tokenizer.swift

@@ -19,6 +19,7 @@ public enum TokenizerError: LocalizedError {
     case missingVocab
     case malformedVocab
     case chatTemplate(String)
+    case missingChatTemplate
     case tooLong(String)
     case mismatchedConfig(String)
 
@@ -36,6 +37,8 @@ public enum TokenizerError: LocalizedError {
             String(localized: "The vocabulary file is malformed or corrupted.", comment: "Error when vocab file is malformed")
         case let .chatTemplate(message):
             String(localized: "Chat template error: \(message)", comment: "Error with chat template")
+        case .missingChatTemplate:
+            String(localized: "This tokenizer does not have a chat template, and no template was passed.")
         case let .tooLong(message):
             String(localized: "Input is too long: \(message)", comment: "Error when input exceeds maximum length")
         case let .mismatchedConfig(message):
@@ -514,7 +517,7 @@ public class PreTrainedTokenizer: Tokenizer {
         }
 
         guard let selectedChatTemplate else {
-            throw TokenizerError.chatTemplate("This tokenizer does not have a chat template, and no template was passed.")
+            throw TokenizerError.missingChatTemplate
         }
 
         let template = try Template(selectedChatTemplate)

Tests/TokenizersTests/ChatTemplateTests.swift

@@ -220,14 +220,16 @@ class ChatTemplateTests: XCTestCase {
     func testApplyTemplateError() async throws {
         let tokenizer = try await AutoTokenizer.from(pretrained: "google-bert/bert-base-uncased")
         XCTAssertFalse(tokenizer.hasChatTemplate)
-        XCTAssertThrowsError(try tokenizer.applyChatTemplate(messages: []))
-        do {
-            _ = try tokenizer.applyChatTemplate(messages: [])
-            XCTFail()
-        } catch let TokenizerError.chatTemplate(message) {
-            XCTAssertEqual(message, "This tokenizer does not have a chat template, and no template was passed.")
-        } catch {
-            XCTFail()
+        XCTAssertThrowsError(try tokenizer.applyChatTemplate(messages: [])) { error in
+            guard let tokenizerError = error as? TokenizerError else {
+                XCTFail("Expected error of type TokenizerError, but got \(type(of: error))")
+                return
+            }
+            if case .missingChatTemplate = tokenizerError {
+                // Correct error caught, test passes
+            } else {
+                XCTFail("Expected .missingChatTemplate, but got \(tokenizerError)")
+            }
         }
     }
 }