diff --git a/tests/backend/specs/easysync/easysync_tests.js b/tests/backend/specs/easysync/easysync_tests.js
index e2f7a5529..c667ffaf3 100644
--- a/tests/backend/specs/easysync/easysync_tests.js
+++ b/tests/backend/specs/easysync/easysync_tests.js
@@ -28,14 +28,13 @@ var helper = require("./helper.js")
 var assert = helper.assert;
 var literal = helper.literal;
 //var throughIterator = helper.throughIterator;
-var assertEqualStrings = helper.assertEqualStrings;
-var assertEqualArrays = helper.assertEqualArrays;
 
 function random() {
   this.nextInt = function (maxValue) {
     return Math.floor(Math.random() * maxValue);
   }
 
+  // maxValue is not used
   this.nextDouble = function (maxValue) {
     return Math.random();
   }
@@ -52,238 +51,8 @@ function random() {
 //    assert("throughSmartAssembler(" + literal(x) + ") == " + literal(x));
 //  })();
 
-  function applyMutations(mu, arrayOfArrays) {
-    arrayOfArrays.forEach(function (a) {
-      var result = mu[a[0]].apply(mu, a.slice(1));
-      if (a[0] == 'remove' && a[3]) {
-        assertEqualStrings(a[3], result);
-      }
-    });
-  }
 
-  function mutationsToChangeset(oldLen, arrayOfArrays) {
-    var assem = Changeset.smartOpAssembler();
-    var op = Changeset.newOp();
-    var bank = Changeset.stringAssembler();
-    var oldPos = 0;
-    var newLen = 0;
-    arrayOfArrays.forEach(function (a) {
-      if (a[0] == 'skip') {
-        op.opcode = '=';
-        op.chars = a[1];
-        op.lines = (a[2] || 0);
-        assem.append(op);
-        oldPos += op.chars;
-        newLen += op.chars;
-      } else if (a[0] == 'remove') {
-        op.opcode = '-';
-        op.chars = a[1];
-        op.lines = (a[2] || 0);
-        assem.append(op);
-        oldPos += op.chars;
-      } else if (a[0] == 'insert') {
-        op.opcode = '+';
-        bank.append(a[1]);
-        op.chars = a[1].length;
-        op.lines = (a[2] || 0);
-        assem.append(op);
-        newLen += op.chars;
-      }
-    });
-    newLen += oldLen - oldPos;
-    assem.endDocument();
-    return Changeset.pack(oldLen, newLen, assem.toString(), bank.toString());
-  }
 
-function runMutationTest(origLines, muts) {
-  var lines1 = origLines.slice();
-  var mu = Changeset.textLinesMutator(lines1);
-  applyMutations(mu, muts);
-  mu.close();
-
-  var inText = origLines.join('');
-  var cs = mutationsToChangeset(inText.length, muts);
-  lines2 = origLines.slice();
-  Changeset.mutateTextLines(cs, lines2);
-
-  var outText = Changeset.applyToText(cs, inText);
-  return [lines1,lines2,outText];
-}
-describe("text line mutations",function(){
-  it("applies mutations to an array of lines #1",function(done){
-    var expected = ["tuple\n", "banana\n", "cream\n", "pie\n", "cabot\n", "bubba\n", "eggplant\n"];
-    var result = runMutationTest(["apple\n", "banana\n", "cabbage\n", "duffle\n", "eggplant\n"], [
-      ['remove', 1, 0, "a"],
-      ['insert', "tu"],
-      ['remove', 1, 0, "p"],
-      ['skip', 4, 1],
-      ['skip', 7, 1],
-      ['insert', "cream\npie\n", 2],
-      ['skip', 2],
-      ['insert', "bot"],
-      ['insert', "\n", 1],
-      ['insert', "bu"],
-      ['skip', 3],
-      ['remove', 3, 1, "ge\n"],
-      ['remove', 6, 0, "duffle"]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  it("applies mutations to an array of lines #2",function(done){
-    var expected = ["tuple\n", "banana\n", "cream\n", "pie\n", "cabot\n", "bubba\n", "eggplant\n"];
-    var result = runMutationTest(["apple\n", "banana\n", "cabbage\n", "duffle\n", "eggplant\n"], [
-      ['remove', 1, 0, "a"],
-      ['remove', 1, 0, "p"],
-      ['insert', "tu"],
-      ['skip', 11, 2],
-      ['insert', "cream\npie\n", 2],
-      ['skip', 2],
-      ['insert', "bot"],
-      ['insert', "\n", 1],
-      ['insert', "bu"],
-      ['skip', 3],
-      ['remove', 3, 1, "ge\n"],
-      ['remove', 6, 0, "duffle"]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  it("applies mutations to an array of lines #3",function(done){
-    var expected = ["banana\n", "cabbage\n", "duffle\n"];
-    var result = runMutationTest(["apple\n", "banana\n", "cabbage\n", "duffle\n", "eggplant\n"], [
-    ['remove', 6, 1, "apple\n"],
-    ['skip', 15, 2],
-    ['skip', 6],
-    ['remove', 1, 1, "\n"],
-    ['remove', 8, 0, "eggplant"],
-    ['skip', 1, 1]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  it("applies mutations to an array of lines #4",function(done){
-    var expected = ["1\n", "2\n", "3\n", "4\n", "5\n"];
-    var result = runMutationTest(["15\n"], [
-    ['skip', 1],
-    ['insert', "\n2\n3\n4\n", 4],
-    ['skip', 2, 1]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  it("applies mutations to an array of lines #5",function(done){
-    var expected = ["15\n"];
-    var result = runMutationTest(["1\n", "2\n", "3\n", "4\n", "5\n"], [
-    ['skip', 1],
-    ['remove', 7, 4, "\n2\n3\n4\n"],
-    ['skip', 2, 1]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  it("applies mutations to an array of lines #6",function(done){
-    var expected = ["0123\n", "abc\n", "xyz\n"];
-    var result = runMutationTest(["123\n", "abc\n", "def\n", "ghi\n", "xyz\n"], [
-    ['insert', "0"],
-    ['skip', 4, 1],
-    ['skip', 4, 1],
-    ['remove', 8, 2, "def\nghi\n"],
-    ['skip', 4, 1]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  it("applies mutations to an array of lines #7",function(done){
-    var expected = ["banana\n", "cabbage\n", "duffle\n"];
-    var result = runMutationTest(["apple\n", "banana\n", "cabbage\n", "duffle\n", "eggplant\n"], [
-    ['remove', 6, 1, "apple\n"],
-    ['skip', 15, 2, true],
-    ['skip', 6, 0, true],
-    ['remove', 1, 1, "\n"],
-    ['remove', 8, 0, "eggplant"],
-    ['skip', 1, 1, true]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-// #2836 regressions
-  xit("applies mutations to an array of lines #8",function(done){
-    var expected = ["foo\n","c"];
-    var result = runMutationTest(["\n","foo\n","\n"], [
-    ['remove', 1, 1, "\n"],
-    ['skip', 4, 1, false],
-    ['remove', 1, 1, "\n"],
-    ['insert',"c"]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  xit("applies mutations to an array of lines #9",function(done){
-    var expected = ["fooc"];
-    var result = runMutationTest(["\n","foo\n","\n"], [
-    ['remove', 1, 1, "\n"],
-    ['skip', 3, 0, false],
-    ['remove', 2, 2, "\n\n"],
-    ['insert',"c"]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  xit("applies mutations to an array of lines #10",function(done){
-    var expected = ["c"]; //TODO find out if c must have a newline because of unknown constraints
-    var result = runMutationTest(["\n"], [
-    ['remove', 1, 1, "\n"],
-    ['insert',"c", 0]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  xit("applies mutations to an array of lines #11",function(done){
-    var expected = ["ac\n"];
-    var result = runMutationTest(["\n"], [
-    ['remove', 1, 1, "\n"],
-    ['insert', "a"],
-    ['insert',"c\n", 1]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-  xit("applies mutations to an array of lines #12",function(done){
-    var expected = ["a\n","c"]; //TODO find out if c must have a newline because of unknown constraints
-    var result = runMutationTest(["\n"], [
-    ['remove', 1, 1, "\n"],
-    ['insert', "a\n", 1], 
-    ['insert',"c"]
-    ]);
-    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
-    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
-    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
-    done()
-  })
-})
 
 
 function poolOrArray(attribs) {
@@ -369,6 +138,7 @@ describe("textLinesMutator",function(){
   function runMutateAttributionTest(testId, attribs, cs, alines, outCorrect) {
     var p = poolOrArray(attribs);
     var alines2 = Array.prototype.slice.call(alines);
+    // result is never used
     var result = Changeset.mutateAttributionLines(
     Changeset.checkRep(cs), alines2, p);
     assertEqualArrays(outCorrect, alines2);
@@ -558,6 +328,7 @@ describe("textLinesMutator",function(){
     // assumes attrib pool like ['apple,','apple,true','banana,','banana,true']
     if (opcode == '-' || rand.nextInt(3)) {
       return '';
+      // branch never taken
     } else if (rand.nextInt(3)) {
       if (opcode == '+' || rand.nextInt(2)) {
         return '*' + Changeset.numToString(rand.nextInt(2) * 2 + 1);
diff --git a/tests/backend/specs/easysync/helper.js b/tests/backend/specs/easysync/helper.js
index c8b82c573..e01980ed6 100644
--- a/tests/backend/specs/easysync/helper.js
+++ b/tests/backend/specs/easysync/helper.js
@@ -17,6 +17,7 @@ exports.assertEqualStrings = function (a, b) {
     return a === b
 }
 
+// not used
 exports.throughIterator = function (opsStr) {
     var iter = Changeset.opIterator(opsStr);
     var assem = Changeset.opAssembler();
@@ -26,6 +27,7 @@ exports.throughIterator = function (opsStr) {
     return assem.toString();
 }
 
+// not used
 exports.throughSmartAssembler =  function (opsStr) {
     var iter = Changeset.opIterator(opsStr);
     var assem = Changeset.smartOpAssembler();
diff --git a/tests/backend/specs/easysync/mutations.js b/tests/backend/specs/easysync/mutations.js
new file mode 100644
index 000000000..099c44a2f
--- /dev/null
+++ b/tests/backend/specs/easysync/mutations.js
@@ -0,0 +1,238 @@
+var Changeset = require("ep_etherpad-lite/static/js/Changeset");
+var helper = require("./helper.js")
+var assertEqualStrings = helper.assertEqualStrings;
+var assertEqualArrays = helper.assertEqualArrays;
+
+describe("text line mutations",function(){
+  it("applies mutations to an array of lines #1",function(done){
+    var expected = ["tuple\n", "banana\n", "cream\n", "pie\n", "cabot\n", "bubba\n", "eggplant\n"];
+    var result = runMutationTest(["apple\n", "banana\n", "cabbage\n", "duffle\n", "eggplant\n"], [
+      ['remove', 1, 0, "a"],
+      ['insert', "tu"],
+      ['remove', 1, 0, "p"],
+      ['skip', 4, 1],
+      ['skip', 7, 1],
+      ['insert', "cream\npie\n", 2],
+      ['skip', 2],
+      ['insert', "bot"],
+      ['insert', "\n", 1],
+      ['insert', "bu"],
+      ['skip', 3],
+      ['remove', 3, 1, "ge\n"],
+      ['remove', 6, 0, "duffle"]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  it("applies mutations to an array of lines #2",function(done){
+    var expected = ["tuple\n", "banana\n", "cream\n", "pie\n", "cabot\n", "bubba\n", "eggplant\n"];
+    var result = runMutationTest(["apple\n", "banana\n", "cabbage\n", "duffle\n", "eggplant\n"], [
+      ['remove', 1, 0, "a"],
+      ['remove', 1, 0, "p"],
+      ['insert', "tu"],
+      ['skip', 11, 2],
+      ['insert', "cream\npie\n", 2],
+      ['skip', 2],
+      ['insert', "bot"],
+      ['insert', "\n", 1],
+      ['insert', "bu"],
+      ['skip', 3],
+      ['remove', 3, 1, "ge\n"],
+      ['remove', 6, 0, "duffle"]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  it("applies mutations to an array of lines #3",function(done){
+    var expected = ["banana\n", "cabbage\n", "duffle\n"];
+    var result = runMutationTest(["apple\n", "banana\n", "cabbage\n", "duffle\n", "eggplant\n"], [
+    ['remove', 6, 1, "apple\n"],
+    ['skip', 15, 2],
+    ['skip', 6],
+    ['remove', 1, 1, "\n"],
+    ['remove', 8, 0, "eggplant"],
+    ['skip', 1, 1]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  it("applies mutations to an array of lines #4",function(done){
+    var expected = ["1\n", "2\n", "3\n", "4\n", "5\n"];
+    var result = runMutationTest(["15\n"], [
+    ['skip', 1],
+    ['insert', "\n2\n3\n4\n", 4],
+    ['skip', 2, 1]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  it("applies mutations to an array of lines #5",function(done){
+    var expected = ["15\n"];
+    var result = runMutationTest(["1\n", "2\n", "3\n", "4\n", "5\n"], [
+    ['skip', 1],
+    ['remove', 7, 4, "\n2\n3\n4\n"],
+    ['skip', 2, 1]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  it("applies mutations to an array of lines #6",function(done){
+    var expected = ["0123\n", "abc\n", "xyz\n"];
+    var result = runMutationTest(["123\n", "abc\n", "def\n", "ghi\n", "xyz\n"], [
+    ['insert', "0"],
+    ['skip', 4, 1],
+    ['skip', 4, 1],
+    ['remove', 8, 2, "def\nghi\n"],
+    ['skip', 4, 1]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  it("applies mutations to an array of lines #7",function(done){
+    var expected = ["banana\n", "cabbage\n", "duffle\n"];
+    var result = runMutationTest(["apple\n", "banana\n", "cabbage\n", "duffle\n", "eggplant\n"], [
+    ['remove', 6, 1, "apple\n"],
+    ['skip', 15, 2, true],
+    ['skip', 6, 0, true],
+    ['remove', 1, 1, "\n"],
+    ['remove', 8, 0, "eggplant"],
+    ['skip', 1, 1, true]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+// #2836 regressions
+  xit("applies mutations to an array of lines #8",function(done){
+    var expected = ["foo\n","c"];
+    var result = runMutationTest(["\n","foo\n","\n"], [
+    ['remove', 1, 1, "\n"],
+    ['skip', 4, 1, false],
+    ['remove', 1, 1, "\n"],
+    ['insert',"c"]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  xit("applies mutations to an array of lines #9",function(done){
+    var expected = ["fooc"];
+    var result = runMutationTest(["\n","foo\n","\n"], [
+    ['remove', 1, 1, "\n"],
+    ['skip', 3, 0, false],
+    ['remove', 2, 2, "\n\n"],
+    ['insert',"c"]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  xit("applies mutations to an array of lines #10",function(done){
+    var expected = ["c"]; //TODO find out if c must have a newline because of unknown constraints
+    var result = runMutationTest(["\n"], [
+    ['remove', 1, 1, "\n"],
+    ['insert',"c", 0]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  xit("applies mutations to an array of lines #11",function(done){
+    var expected = ["ac\n"];
+    var result = runMutationTest(["\n"], [
+    ['remove', 1, 1, "\n"],
+    ['insert', "a"],
+    ['insert',"c\n", 1]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+  xit("applies mutations to an array of lines #12",function(done){
+    var expected = ["a\n","c"]; //TODO find out if c must have a newline because of unknown constraints
+    var result = runMutationTest(["\n"], [
+    ['remove', 1, 1, "\n"],
+    ['insert', "a\n", 1], 
+    ['insert',"c"]
+    ]);
+    if (!assertEqualArrays(result[0], expected)) throw new Error("textLinesMutator result is wrong: expected "+expected+" got "+result[0]);
+    if (!assertEqualArrays(result[1], expected)) throw new Error("mutateTextLines result is wrong: expected "+expected+" got "+result[1]);
+    if (!assertEqualStrings(result[2], expected.join(''))) throw new Error('applyToText result is wrong: expected '+expected.join('')+" got "+result[2]);
+    done()
+  })
+})
+
+function runMutationTest(origLines, muts) {
+  var lines1 = origLines.slice();
+  var mu = Changeset.textLinesMutator(lines1);
+  applyMutations(mu, muts);
+  mu.close();
+
+  var inText = origLines.join('');
+  var cs = mutationsToChangeset(inText.length, muts);
+  lines2 = origLines.slice();
+  Changeset.mutateTextLines(cs, lines2);
+
+  var outText = Changeset.applyToText(cs, inText);
+  return [lines1,lines2,outText];
+}
+
+function applyMutations(mu, arrayOfArrays) {
+  arrayOfArrays.forEach(function (a) {
+    var result = mu[a[0]].apply(mu, a.slice(1));
+    if (a[0] == 'remove' && a[3]) {
+      assertEqualStrings(a[3], result);
+    }
+  });
+}
+
+function mutationsToChangeset(oldLen, arrayOfArrays) {
+  var assem = Changeset.smartOpAssembler();
+  var op = Changeset.newOp();
+  var bank = Changeset.stringAssembler();
+  var oldPos = 0;
+  var newLen = 0;
+  arrayOfArrays.forEach(function (a) {
+    if (a[0] == 'skip') {
+      op.opcode = '=';
+      op.chars = a[1];
+      op.lines = (a[2] || 0);
+      assem.append(op);
+      oldPos += op.chars;
+      newLen += op.chars;
+    } else if (a[0] == 'remove') {
+      op.opcode = '-';
+      op.chars = a[1];
+      op.lines = (a[2] || 0);
+      assem.append(op);
+      oldPos += op.chars;
+    } else if (a[0] == 'insert') {
+      op.opcode = '+';
+      bank.append(a[1]);
+      op.chars = a[1].length;
+      op.lines = (a[2] || 0);
+      assem.append(op);
+      newLen += op.chars;
+    }
+  });
+  newLen += oldLen - oldPos;
+  assem.endDocument();
+  return Changeset.pack(oldLen, newLen, assem.toString(), bank.toString());
+}