diff --git a/Jakefile b/Jakefile
index 2cef554cc75..2efd973a021 100644
--- a/Jakefile
+++ b/Jakefile
@@ -144,7 +144,8 @@ var harnessSources = [
     "services/colorization.ts",
     "services/documentRegistry.ts",
     "services/preProcessFile.ts",
-    "services/patternMatcher.ts"
+    "services/patternMatcher.ts",
+    "versionCache.ts"
 ].map(function (f) {
     return path.join(unittestsDirectory, f);
 })).concat([
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index a3814c8fec1..366e4dbfd84 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -1466,6 +1466,10 @@ module ts.server {
             return accum;
         }
 
+        getLength(): number {
+            return this.root.charCount();
+        }
+
         every(f: (ll: LineLeaf, s: number, len: number) => boolean, rangeStart: number, rangeEnd?: number) {
             if (!rangeEnd) {
                 rangeEnd = this.root.charCount();
diff --git a/tests/cases/unittests/versionCache.ts b/tests/cases/unittests/versionCache.ts
new file mode 100644
index 00000000000..12cf9c1b817
--- /dev/null
+++ b/tests/cases/unittests/versionCache.ts
@@ -0,0 +1,279 @@
+/// <reference path="..\..\..\src\harness\harness.ts" />
+/// <reference path="..\..\..\src\server\editorServices.ts" />
+
+module ts {
+    function editFlat(position: number, deletedLength: number, newText: string, source: string) {
+        return source.substring(0, position) + newText + source.substring(position + deletedLength, source.length);
+    }
+
+    function lineColToPosition(lineIndex: server.LineIndex, line: number, col: number) {
+        var lineInfo = lineIndex.lineNumberToInfo(line);
+        return (lineInfo.offset + col - 1);
+    }
+
+    function validateEdit(lineIndex: server.LineIndex, sourceText: string, position: number, deleteLength: number, insertString: string): void {
+        let checkText = editFlat(position, deleteLength, insertString, sourceText);
+        let snapshot = lineIndex.edit(position, deleteLength, insertString);
+        let editedText = snapshot.getText(0, snapshot.getLength());
+
+        assert.equal(editedText, checkText);
+    }
+
+    describe('VersionCache TS code', () => {
+        var testContent = `/// <reference path="z.ts" />
+var x = 10;
+var y = { zebra: 12, giraffe: "ell" };
+z.a;
+class Point {
+    x: number;
+}
+k=y;
+var p:Point=new Point();
+var q:Point=<Point>p;`
+
+        let {lines, lineMap} = server.LineIndex.linesFromText(testContent);
+        assert.isTrue(lines.length > 0, "Failed to initialize test text. Expected text to have at least one line");
+
+        let lineIndex = new server.LineIndex();
+        lineIndex.load(lines);
+
+        function validateEditAtLineCharIndex(line: number, char: number, deleteLength: number, insertString: string): void {
+            let position = lineColToPosition(lineIndex, line, char);
+            validateEdit(lineIndex, testContent, position, deleteLength, insertString);
+        }
+
+        it('change 9 1 0 1 {"y"}', () => {
+            validateEditAtLineCharIndex(9, 1, 0, "y");
+        });
+
+        it('change 9 2 0 1 {"."}', () => {
+            validateEditAtLineCharIndex(9, 2, 0, ".");
+        });
+
+        it('change 9 3 0 1 {"\\n"}', () => {
+            validateEditAtLineCharIndex(9, 3, 0, "\n");
+        });
+
+        it('change 10 1 0 10 {"\\n\\n\\n\\n\\n\\n\\n\\n\\n\\n"}', () => {
+            validateEditAtLineCharIndex(10, 1, 0, "\n\n\n\n\n\n\n\n\n\n");
+        });
+
+        it('change 19 1 1 0', () => {
+            validateEditAtLineCharIndex(19, 1, 1, "");
+        });
+
+        it('change 18 1 1 0', () => {
+            validateEditAtLineCharIndex(18, 1, 1, "");
+        });
+    });
+
+    describe('VersionCache simple text', () => {
+        let testContent = `in this story:
+the lazy brown fox
+jumped over the cow
+that ate the grass
+that was purple at the tips
+and grew 1cm per day`;
+
+        let {lines, lineMap} = server.LineIndex.linesFromText(testContent);
+        assert.isTrue(lines.length > 0, "Failed to initialize test text. Expected text to have at least one line");
+
+        let lineIndex = new server.LineIndex();
+        lineIndex.load(lines);
+
+        function validateEditAtPosition(position: number, deleteLength: number, insertString: string): void {
+            validateEdit(lineIndex, testContent, position, deleteLength, insertString);
+        }
+
+        it('Insert at end of file', () => {
+            validateEditAtPosition(testContent.length, 0, "hmmmm...\r\n");
+        });
+
+        it('Unusual line endings merge', () => {
+            validateEditAtPosition(lines[0].length - 1, lines[1].length, "");
+        });
+
+        it('Delete whole line and nothing but line (last line)', () => {
+            validateEditAtPosition(lineMap[lineMap.length - 2], lines[lines.length - 1].length, "");
+        });
+
+        it('Delete whole line and nothing but line (first line)', () => {
+            validateEditAtPosition(0, lines[0].length, "");
+        });
+
+        it('Delete whole line (first line) and insert with no line breaks', () => {
+            validateEditAtPosition(0, lines[0].length, "moo, moo, moo! ");
+        });
+
+        it('Delete whole line (first line) and insert with multiple line breaks', () => {
+            validateEditAtPosition(0, lines[0].length, "moo, \r\nmoo, \r\nmoo! ");
+        });
+
+        it('Delete multiple lines and nothing but lines (first and second lines)', () => {
+            validateEditAtPosition(0, lines[0].length + lines[1].length, "");
+        });
+
+        it('Delete multiple lines and nothing but lines (second and third lines)', () => {
+            validateEditAtPosition(lines[0].length, lines[1].length + lines[2].length, "");
+        });
+
+        it('Insert multiple line breaks', () => {
+            validateEditAtPosition(21, 1, "cr...\r\ncr...\r\ncr...\r\ncr...\r\ncr...\r\ncr...\r\ncr...\r\ncr...\r\ncr...\r\ncr...\r\ncr...\r\ncr");
+        });
+
+        it('Insert multiple line breaks', () => {
+            validateEditAtPosition(21, 1, "cr...\r\ncr...\r\ncr");
+        });
+
+        it('Insert multiple line breaks with leading \\n', () => {
+            validateEditAtPosition(21, 1, "\ncr...\r\ncr...\r\ncr");
+        });
+
+        it('Single line no line breaks deleted or inserted, delete 1 char', () => {
+            validateEditAtPosition(21, 1, "");
+        });
+
+        it('Single line no line breaks deleted or inserted, insert 1 char', () => {
+            validateEditAtPosition(21, 0, "b");
+        });
+
+        it('Single line no line breaks deleted or inserted, delete 1, insert 2 chars', () => {
+            validateEditAtPosition(21, 1, "cr");
+        });
+
+        it('Delete across line break (just the line break)', () => {
+            validateEditAtPosition(21, 22, "");
+        });
+
+        it('Delete across line break', () => {
+            validateEditAtPosition(21, 32, "");
+        });
+
+        it('Delete across multiple line breaks and insert no line breaks', () => {
+            validateEditAtPosition(21, 42, "");
+        });
+
+        it('Delete across multiple line breaks and insert text', () => {
+            validateEditAtPosition(21, 42, "slithery ");
+        });
+    });
+
+    describe('VersionCache stress test', () => {
+        const iterationCount = 20;
+        //const interationCount = 20000; // uncomment for testing
+
+        // Use scanner.ts, decent size, does not change frequentlly
+        let testFileName = "src/compiler/scanner.ts";
+        let testContent = Harness.IO.readFile(testFileName);
+        let totalChars = testContent.length;
+        assert.isTrue(totalChars > 0, "Failed to read test file.");
+
+        let {lines, lineMap} = server.LineIndex.linesFromText(testContent);
+        assert.isTrue(lines.length > 0, "Failed to initialize test text. Expected text to have at least one line");
+
+        let lineIndex = new server.LineIndex();
+        lineIndex.load(lines);
+
+        let rsa: number[] = [];
+        let la: number[] = [];
+        let las: number[] = [];
+        let elas: number[] = [];
+        let ersa: number[] = [];
+        let ela: number[] = [];
+        let etotalChars = totalChars;
+
+        for (let j = 0; j < 100000; j++) {
+            rsa[j] = Math.floor(Math.random() * totalChars);
+            la[j] = Math.floor(Math.random() * (totalChars - rsa[j]));
+            if (la[j] > 4) {
+                las[j] = 4;
+            }
+            else {
+                las[j] = la[j];
+            }
+            if (j < 4000) {
+                ersa[j] = Math.floor(Math.random() * etotalChars);
+                ela[j] = Math.floor(Math.random() * (etotalChars - ersa[j]));
+                if (ela[j] > 4) {
+                    elas[j] = 4;
+                }
+                else {
+                    elas[j] = ela[j];
+                }
+                etotalChars += (las[j] - elas[j]);
+            }
+        }
+
+        it("Range (average length 1/4 file size)", () => {
+            for (let i = 0; i < iterationCount; i++) {
+                let s2 = lineIndex.getText(rsa[i], la[i]);
+                let s1 = testContent.substring(rsa[i], rsa[i] + la[i]);
+                assert.equal(s1, s2);
+            }
+        });
+
+        it("Range (average length 4 chars)", () => {
+            for (let j = 0; j < iterationCount; j++) {
+                let s2 = lineIndex.getText(rsa[j], las[j]);
+                let s1 = testContent.substring(rsa[j], rsa[j] + las[j]);
+                assert.equal(s1, s2);
+            }
+        });
+
+        it("Edit (average length 4)", () => {
+            for (let i = 0; i < iterationCount; i++) {
+                let insertString = testContent.substring(rsa[100000 - i], rsa[100000 - i] + las[100000 - i]);
+                let snapshot = lineIndex.edit(rsa[i], las[i], insertString);
+                let checkText = editFlat(rsa[i], las[i], insertString, testContent);
+                let snapText = snapshot.getText(0, checkText.length);
+                assert.equal(checkText, snapText);
+            }
+        });
+
+        it("Edit ScriptVersionCache ", () => {
+            let svc = server.ScriptVersionCache.fromString(testContent);
+            let checkText = testContent;
+
+            for (let i = 0; i < iterationCount; i++) {
+                let insertString = testContent.substring(rsa[i], rsa[i] + las[i]);
+                svc.edit(ersa[i], elas[i], insertString);
+                checkText = editFlat(ersa[i], elas[i], insertString, checkText);
+                if (0 == (i % 4)) {
+                    let snap = svc.getSnapshot();
+                    let snapText = snap.getText(0, checkText.length);
+                    assert.equal(checkText, snapText);
+                }
+            }
+        });
+
+        it("Edit (average length 1/4th file size)", () => {
+            for (let i = 0; i < iterationCount; i++) {
+                let insertString = testContent.substring(rsa[100000 - i], rsa[100000 - i] + la[100000 - i]);
+                let snapshot = lineIndex.edit(rsa[i], la[i], insertString);
+                let checkText = editFlat(rsa[i], la[i], insertString, testContent);
+                let snapText = snapshot.getText(0, checkText.length);
+                assert.equal(checkText, snapText);
+            }
+        });
+
+        it("Line/offset from pos", () => {
+            for (let i = 0; i < iterationCount; i++) {
+                let lp = lineIndex.charOffsetToLineNumberAndPos(rsa[i]);
+                let lac = ts.computeLineAndCharacterOfPosition(lineMap, rsa[i]);
+                assert.equal(lac.line + 1, lp.line, "Line number mismatch " + (lac.line + 1) + " " + lp.line + " " + i);
+                assert.equal(lac.character, (lp.offset), "Charachter offset mismatch " + lac.character + " " + lp.offset + " " + i);
+            }
+        });
+
+        it("Start pos from line", () => {
+            for (let i = 0; i < iterationCount; i++) {
+                for (let j = 0, llen = lines.length; j < llen; j++) {
+                    let lineInfo = lineIndex.lineNumberToInfo(j + 1);
+                    let lineIndexOffset = lineInfo.offset;
+                    let lineMapOffset = lineMap[j];
+                    assert.equal(lineIndexOffset, lineMapOffset);
+                }
+            }
+        });
+    });
+}