diff --git a/src/components/TracePage/TraceTimelineViewer/utils.test.js b/src/components/TracePage/TraceTimelineViewer/utils.test.js
index 5160f7ead9..227a6eacde 100644
--- a/src/components/TracePage/TraceTimelineViewer/utils.test.js
+++ b/src/components/TracePage/TraceTimelineViewer/utils.test.js
@@ -18,10 +18,95 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
-import { spanContainsErredSpan } from './utils';
+import {
+  calculateSpanPosition,
+  calculateTimeAtPositon,
+  convertTimeRangeToPercent,
+  ensureWithinRange,
+  hasTagKey,
+  isClientSpan,
+  isErrorSpan,
+  isServerSpan,
+  spanContainsErredSpan,
+} from './utils';
 import traceGenerator from '../../../demo/trace-generators';
 
-it('spanContainsErredSpan(...) is true only when a descendant has an error tag', () => {
+it('calculateSpanPosition() maps a sub-range to percents with a zoom applied', () => {
+  const args = {
+    traceStartTime: 100,
+    traceEndTime: 200,
+    xStart: 0,
+    xEnd: 50,
+  };
+
+  args.spanStart = 100;
+  args.spanEnd = 200;
+  expect(calculateSpanPosition(args)).toEqual({ xStart: 0, xEnd: 200 });
+
+  args.spanStart = 100;
+  args.spanEnd = 150;
+  expect(calculateSpanPosition(args)).toEqual({ xStart: 0, xEnd: 100 });
+
+  args.spanStart = 150;
+  args.spanEnd = 200;
+  expect(calculateSpanPosition(args)).toEqual({ xStart: 100, xEnd: 200 });
+});
+
+it('calculateTimeAtPositon() converts a percent to a value in [0, duration]', () => {
+  const traceDuration = 1000;
+  expect(calculateTimeAtPositon({ position: 0, traceDuration })).toBe(0);
+  expect(calculateTimeAtPositon({ position: 100, traceDuration })).toBe(
+    traceDuration
+  );
+  expect(calculateTimeAtPositon({ position: 50, traceDuration })).toBe(
+    0.5 * traceDuration
+  );
+});
+
+it('convertTimeRangeToPercent() converts a sub-range to percent start and end values', () => {
+  const traceRange = [100, 200];
+  expect(convertTimeRangeToPercent([100, 200], traceRange)).toEqual([0, 100]);
+  expect(convertTimeRangeToPercent([199, 200], traceRange)).toEqual([99, 100]);
+  expect(convertTimeRangeToPercent([100, 101], traceRange)).toEqual([0, 1]);
+  expect(convertTimeRangeToPercent([100, 150], traceRange)).toEqual([0, 50]);
+  expect(convertTimeRangeToPercent([0, 250], traceRange)).toEqual([-100, 150]);
+});
+
+it('ensureWithinRange() clamps numeric values', () => {
+  const min = 10;
+  const max = 20;
+  expect(ensureWithinRange([min, max], -1)).toBe(10);
+  expect(ensureWithinRange([min, max], 0)).toBe(10);
+  expect(ensureWithinRange([min, max], 15)).toBe(15);
+  expect(ensureWithinRange([min, max], 25)).toBe(20);
+  expect(isNaN(ensureWithinRange([min, max], NaN))).toBe(true);
+});
+
+it('hasTagKey() returns true iff the key/value pair is found', () => {
+  const tags = traceGenerator.tags();
+  tags.push({ key: 'span.kind', value: 'server' });
+  expect(hasTagKey([], 'span.kind', 'client')).toBe(false);
+  expect(hasTagKey(tags, 'span.kind', 'client')).toBe(false);
+  expect(hasTagKey(tags, 'span.kind', 'server')).toBe(true);
+});
+
+const spanTypeTestCases = [
+  { fn: isClientSpan, name: 'isClientSpan', key: 'span.kind', value: 'client' },
+  { fn: isServerSpan, name: 'isServerSpan', key: 'span.kind', value: 'server' },
+  { fn: isErrorSpan, name: 'isErrorSpan', key: 'error', value: true },
+];
+
+spanTypeTestCases.forEach(testCase => {
+  const msg = `${testCase.name}() is true only when a ${testCase.key}=${testCase.value} tag is present`;
+  it(msg, () => {
+    const span = { tags: traceGenerator.tags() };
+    expect(testCase.fn(span)).toBe(false);
+    span.tags.push(testCase);
+    expect(testCase.fn(span)).toBe(true);
+  });
+});
+
+it('spanContainsErredSpan() is true only when a descendant has an error tag', () => {
   const errorTag = { key: 'error', type: 'bool', value: true };
   const getTags = withError =>
     withError ? traceGenerator.tags().concat(errorTag) : traceGenerator.tags();
diff --git a/src/components/TracePage/index.js b/src/components/TracePage/index.js
index 7277abf4ab..a276bc717e 100644
--- a/src/components/TracePage/index.js
+++ b/src/components/TracePage/index.js
@@ -120,6 +120,9 @@ export default class TracePage extends Component {
 
   toggleSlimView(slimView) {
     this.setState({ slimView });
+    // fix issue #12 - TraceView header expander not working correctly
+    // TODO: evaluate alternatives to react-sticky
+    setTimeout(() => this.forceUpdate(), 0);
   }
 
   ensureTraceFetched() {