diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index f51e492d6b5..b6f21d91333 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -112,58 +112,37 @@ module Utils {
         });
     }
 
-    export function checkInvariants(node: ts.Node, parent: ts.Node): void {
-        if(node) {
-            if (node.pos < 0) {
-                throw new Error("node.pos < 0");
-            }
-            if (node.end < 0) {
-                throw new Error("node.end < 0");
-            }
-            if (node.end < node.pos) {
-                throw new Error("node.end < node.pos");
-            }
-            if (node.parent !== parent) {
-                throw new Error("node.parent !== parent");
-            }
+    export function assertInvariants(node: ts.Node, parent: ts.Node): void {
+        if (node) {
+            assert.isFalse(node.pos < 0, "node.pos < 0");
+            assert.isFalse(node.end < 0, "node.end < 0");
+            assert.isFalse(node.end < node.pos, "node.end < node.pos");
+            assert.equal(node.parent, parent, "node.parent !== parent");
+
             if (parent) {
                 // Make sure each child is contained within the parent.
-                if (node.pos < parent.pos) {
-                    throw new Error("node.pos < parent.pos");
-                }
-                if (node.end > parent.end) {
-                    throw new Error("node.end > parent.end");
-                }
+                assert.isFalse(node.pos < parent.pos, "node.pos < parent.pos");
+                assert.isFalse(node.end > parent.end, "node.end > parent.end");
             }
 
             ts.forEachChild(node, child => {
-                checkInvariants(child, node);
+                assertInvariants(child, node);
             });
 
             // Make sure each of the children is in order.
             var currentPos = 0;
             ts.forEachChild(node,
                 child => {
-                    if (child.pos < currentPos) {
-                        throw new Error("child.pos < currentPos");
-                    }
+                    assert.isFalse(child.pos < currentPos, "child.pos < currentPos");
                     currentPos = child.end;
                 },
                 (array: ts.NodeArray<ts.Node>) => {
-                    if (array.pos < node.pos) {
-                        throw new Error("array.pos < node.pos");
-                    }
-                    if (array.end > node.end) {
-                        throw new Error("array.end > node.end");
-                    }
+                    assert.isFalse(array.pos < node.pos, "array.pos < node.pos");
+                    assert.isFalse(array.end > node.end, "array.end > node.end");
+                    assert.isFalse(array.pos < currentPos, "array.pos < currentPos");
 
-                    if (array.pos < currentPos) {
-                        throw new Error("array.pos < currentPos");
-                    }
                     for (var i = 0, n = array.length; i < n; i++) {
-                        if (array[i].pos < currentPos) {
-                            throw new Error("array[i].pos < currentPos");
-                        }
+                        assert.isFalse(array[i].pos < currentPos, "array[i].pos < currentPos");
                         currentPos = array[i].end
                     }
 
@@ -179,9 +158,8 @@ module Utils {
                 }
                 var child = (<any>node)[childName];
                 if (isNodeOrArray(child)) {
-                    if (childNodesAndArrays.indexOf(child) < 0) {
-                        throw new Error("Child when forEach'ing over node. " + (<any>ts).SyntaxKind[node.kind] + "-" + childName);
-                    }
+                    assert.isFalse(childNodesAndArrays.indexOf(child) < 0,
+                        "Missing child when forEach'ing over node: " + (<any>ts).SyntaxKind[node.kind] + "-" + childName);
                 }
             }
         }
diff --git a/src/harness/test262Runner.ts b/src/harness/test262Runner.ts
index f9c083a2542..b53011237b7 100644
--- a/src/harness/test262Runner.ts
+++ b/src/harness/test262Runner.ts
@@ -189,7 +189,7 @@ class Test262BaselineRunner extends RunnerBase {
 
             it('satisfies invariants', () => {
                 var sourceFile = testState.checker.getProgram().getSourceFile(Test262BaselineRunner.getTestFilePath(testState.filename));
-                Utils.checkInvariants(sourceFile, /*parent:*/ undefined);
+                Utils.assertInvariants(sourceFile, /*parent:*/ undefined);
             });
 
             it('has the expected AST',() => {
diff --git a/tests/cases/unittests/incrementalParser.ts b/tests/cases/unittests/incrementalParser.ts
index 440ffc99f7d..f1e59809400 100644
--- a/tests/cases/unittests/incrementalParser.ts
+++ b/tests/cases/unittests/incrementalParser.ts
@@ -31,25 +31,25 @@ module ts {
     // are still ok and we're still appropriately reusing most of the tree.
     function compareTrees(oldText: IScriptSnapshot, newText: IScriptSnapshot, textChangeRange: TextChangeRange, expectedReusedElements: number, oldTree?: SourceFile): SourceFile {
         oldTree = oldTree || createTree(oldText, /*version:*/ ".");
-        Utils.checkInvariants(oldTree, /*parent:*/ undefined);
+        Utils.assertInvariants(oldTree, /*parent:*/ undefined);
 
         // Create a tree for the new text, in a non-incremental fashion.
         var newTree = createTree(newText, oldTree.version + ".");
-        Utils.checkInvariants(newTree, /*parent:*/ undefined);
+        Utils.assertInvariants(newTree, /*parent:*/ undefined);
 
         // Create a tree for the new text, in an incremental fashion.
         var incrementalNewTree = oldTree.update(newText, oldTree.version + ".", /*isOpen:*/ true, textChangeRange);
-        Utils.checkInvariants(incrementalNewTree, /*parent:*/ undefined);
+        Utils.assertInvariants(incrementalNewTree, /*parent:*/ undefined);
 
         // We should get the same tree when doign a full or incremental parse.
         assertStructuralEquals(newTree, incrementalNewTree);
 
         // There should be no reused nodes between two trees that are fully parsed.
-        Debug.assert(reusedElements(oldTree, newTree) === 0);
+        assert.isTrue(reusedElements(oldTree, newTree) === 0);
 
         if (expectedReusedElements !== -1) {
             var actualReusedCount = reusedElements(oldTree, incrementalNewTree);
-            Debug.assert(actualReusedCount === expectedReusedElements, actualReusedCount + " !== " + expectedReusedElements);
+            assert.equal(actualReusedCount, expectedReusedElements, actualReusedCount + " !== " + expectedReusedElements);
         }
 
         return incrementalNewTree;
@@ -60,29 +60,13 @@ module ts {
             return;
         }
 
-        if (!node1 || !node2) {
-            throw new Error("!node1 || !node2");
-        }
-
-        if (node1.pos !== node2.pos) {
-            throw new Error("node1.pos !== node2.pos");
-        }
-
-        if (node1.end !== node2.end) {
-            throw new Error("node1.end !== node2.end");
-        }
-
-        if (node1.kind !== node2.kind) {
-            throw new Error("node1.kind !== node2.kind");
-        }
-
-        if (node1.flags !== node2.flags) {
-            throw new Error("node1.flags !== node2.flags");
-        }
-
-        if (node1.parserContextFlags !== node2.parserContextFlags) {
-            throw new Error("node1.parserContextFlags !== node2.parserContextFlags");
-        }
+        assert(node1, "node1");
+        assert(node2, "node2");
+        assert.equal(node1.pos, node2.pos, "node1.pos !== node2.pos");
+        assert.equal(node1.end, node2.end, "node1.end !== node2.end");
+        assert.equal(node1.kind, node2.kind, "node1.kind !== node2.kind");
+        assert.equal(node1.flags, node2.flags, "node1.flags !== node2.flags");
+        assert.equal(node1.parserContextFlags, node2.parserContextFlags, "node1.parserContextFlags !== node2.parserContextFlags");
 
         forEachChild(node1,
             child1 => {
@@ -104,21 +88,11 @@ module ts {
             return;
         }
 
-        if (!array1 || !array2) {
-            throw new Error("!array1 || !array2");
-        }
-
-        if (array1.pos !== array2.pos) {
-            throw new Error("array1.pos !== array2.pos");
-        }
-
-        if (array1.end !== array2.end) {
-            throw new Error("array1.end !== array2.end");
-        }
-
-        if (array1.length !== array2.length) {
-            throw new Error("array1.length !== array2.length");
-        }
+        assert(array1, "array1");
+        assert(array2, "array2");
+        assert.equal(array1.pos, array2.pos, "array1.pos !== array2.pos");
+        assert.equal(array1.end, array2.end, "array1.end !== array2.end");
+        assert.equal(array1.length, array2.length, "array1.length !== array2.length");
 
         for (var i = 0, n = array1.length; i < n; i++) {
             assertStructuralEquals(array1[i], array2[i]);