Fix flaky test causing spurious drops in code coverage (#1632)

## Which problem is this PR solving?
- Resolves #1489

## Short description of the changes
- To remove the non determinism in the code 

---------

Signed-off-by: GLVS Kiriti <glvskiriti2003369@gmail.com>
Co-authored-by: Yuri Shkuro <yurishkuro@users.noreply.github.com>

packages/jaeger-ui/src/components/TracePage/TraceTimelineViewer/SpanBarRow.test.js

@@ -42,7 +42,10 @@ describe('<SpanBarRow>', () => {
       serviceName: 'rpc-service-name',
     },
     showErrorIcon: false,
-    getViewedBounds: () => ({ start: 0, end: 1 }),
+    getViewedBounds: jest
+      .fn()
+      .mockReturnValueOnce({ start: 0.5, end: 0.6 })
+      .mockReturnValue({ start: 0, end: 1 }),
     span: {
       duration: 'test-duration',
       hasChildren: true,