Add tests.

Packages/NSStringUtils/Tests/NSStringUtilsTests/NSStringUtilsTests.swift

@@ -2,6 +2,17 @@ import XCTest
 @testable import NSStringUtils
 
 final class NSStringUtilsTests: XCTestCase {
+
+    func testNextNormal_0() {
+        let s = NSString("中文")
+        XCTAssertEqual(s.nextUtf16Position(for: 0), 1)
+    }
+
+    func testNextNormal_1() {
+        let s = NSString("中文")
+        XCTAssertEqual(s.nextUtf16Position(for: 1), 2)
+    }
+
     func testNextWith🌳_0() {
         let s = NSString("🌳🌳")
         XCTAssertEqual(s.nextUtf16Position(for: 0), 2)
@@ -32,6 +43,16 @@ final class NSStringUtilsTests: XCTestCase {
         XCTAssertEqual(s.nextUtf16Position(for: 4), 6)
     }
 
+    func testPrevNormal_0() {
+        let s = NSString("中文")
+        XCTAssertEqual(s.previousUtf16Position(for: 1), 0)
+    }
+
+    func testPrevNormal_1() {
+        let s = NSString("中文")
+        XCTAssertEqual(s.previousUtf16Position(for: 2), 1)
+    }
+
     func testPrevWith🌳_0() {
         let s = NSString("🌳🌳")
         XCTAssertEqual(s.previousUtf16Position(for: 0), 0)
@@ -42,17 +63,17 @@ final class NSStringUtilsTests: XCTestCase {
         XCTAssertEqual(s.previousUtf16Position(for: 1), 0)
     }
 
-    func testINextWith🌳_2() {
+    func testPrevWith🌳_2() {
         let s = NSString("🌳🌳")
         XCTAssertEqual(s.previousUtf16Position(for: 2), 0)
     }
 
-    func testINextWith🌳_3() {
+    func testPrevWith🌳_3() {
         let s = NSString("🌳🌳")
         XCTAssertEqual(s.previousUtf16Position(for: 3), 0)
     }
 
-    func testINextWith🌳_4() {
+    func testPrevWith🌳_4() {
         let s = NSString("🌳🌳")
         XCTAssertEqual(s.previousUtf16Position(for: 4), 2)
     }

Source/KeyHandler.mm

@@ -577,7 +577,7 @@ static NSString *const kGraphVizOutputfile = @"/tmp/McBopomofo-visualization.dot
     if ([input isShiftHold]) {
         // Shift + left
         if (currentState.cursorIndex > 0) {
-            NSInteger previousPosition = [currentState.composingBuffer nextUtf16PositionFor:currentState.cursorIndex];
+            NSInteger previousPosition = [currentState.composingBuffer previousUtf16PositionFor:currentState.cursorIndex];
             InputStateMarking *marking = [[InputStateMarking alloc] initWithComposingBuffer:currentState.composingBuffer cursorIndex:currentState.cursorIndex markerIndex:previousPosition readings:[self _currentReadings]];
             marking.tooltipForInputting = currentState.tooltip;
             stateCallback(marking);