test: verify characters at positions in posFromIndex tests

Add expectCharAtIndex helper that checks both the returned position
and the actual character at that position, making the tests more
robust against regressions.

Author: abose

test/spec/Document-test.js

@@ -237,10 +237,11 @@ define(function (require, exports, module) {
         });
 
         describe("posFromIndex", function () {
+            const TEST_CONTENT = "line0\nline1\nline2\n";
             let myEditor, myDocument;
 
             beforeEach(function () {
-                const mocks = SpecRunnerUtils.createMockEditor("line0\nline1\nline2\n", "unknown");
+                const mocks = SpecRunnerUtils.createMockEditor(TEST_CONTENT, "unknown");
                 myDocument = mocks.doc;
                 myEditor = mocks.editor;
             });
@@ -253,29 +254,36 @@ define(function (require, exports, module) {
                 }
             });
 
+            // Verify the character at a given index matches the char at the returned position
+            function expectCharAtIndex(index, expectedChar) {
+                const pos = myDocument.posFromIndex(index);
+                const actualChar = myDocument.getLine(pos.line).charAt(pos.ch);
+                expect(actualChar).toBe(expectedChar);
+                return pos;
+            }
+
             it("should return {0,0} for index 0", function () {
-                const pos = myDocument.posFromIndex(0);
+                const pos = expectCharAtIndex(0, "l");
                 expect(pos.line).toBe(0);
                 expect(pos.ch).toBe(0);
             });
 
             it("should return correct position within first line", function () {
-                // "line0" — index 3 is 'e'
-                const pos = myDocument.posFromIndex(3);
+                const pos = expectCharAtIndex(3, "e");
                 expect(pos.line).toBe(0);
                 expect(pos.ch).toBe(3);
             });
 
             it("should return start of second line after newline", function () {
-                // "line0\n" is 6 chars, so index 6 is start of line 1
-                const pos = myDocument.posFromIndex(6);
+                // "line0\n" is 6 chars, so index 6 is 'l' at start of "line1"
+                const pos = expectCharAtIndex(6, "l");
                 expect(pos.line).toBe(1);
                 expect(pos.ch).toBe(0);
             });
 
             it("should return correct position on third line", function () {
                 // "line0\nline1\n" is 12 chars, index 14 is 'n' in "line2"
-                const pos = myDocument.posFromIndex(14);
+                const pos = expectCharAtIndex(14, "n");
                 expect(pos.line).toBe(2);
                 expect(pos.ch).toBe(2);
             });
@@ -286,20 +294,23 @@ define(function (require, exports, module) {
                 SpecRunnerUtils.destroyMockEditor(myDocument);
                 myEditor = null;
 
-                // Content is "line0\nline1\nline2\n" — same as beforeEach
                 expect(myDocument._masterEditor).toBe(null);
 
+                // Verify against raw string since getLine is unavailable without editor
                 let pos = myDocument.posFromIndex(0);
                 expect(pos.line).toBe(0);
                 expect(pos.ch).toBe(0);
+                expect(TEST_CONTENT[0]).toBe("l");
 
                 pos = myDocument.posFromIndex(6);
                 expect(pos.line).toBe(1);
                 expect(pos.ch).toBe(0);
+                expect(TEST_CONTENT[6]).toBe("l");
 
                 pos = myDocument.posFromIndex(14);
                 expect(pos.line).toBe(2);
                 expect(pos.ch).toBe(2);
+                expect(TEST_CONTENT[14]).toBe("n");
             });
         });
     });