Build a simple test tube. A few steps but these methods can be quite useful for other things that you will build. Keys to this is using the Make Compound Path and the Exclude Overlap in the Pathfinder Panel.
Have fun with this one!
Start with a rectangle. Fill it with a color, no stroke.
Use the Direct Selection Tool to select just the lower two corners of the rectangle. With the Live Corner targets active, drag the targets into the center of the rectangle until it stops. This will round the lower corners.
Add a 10 pt line at the top of the test tube. Align the center with the center of the rectangle. Use the Rounded End feature in the Stroke Panel to round the line ends.
Duplicate the line on top of the test tube off to the side. (I colored it green to make it more visible). OPTIN + CLICK & DRAG the green line down, then COMMAND +D until you get several lines.
Select all the green lines and outline them all. Object > Path> Outline Stroke. This will turn it into shapes rather than lines, this is important when you use the Pathfinder Panel. Shapes and lines don't work well together, everything has to be shapes, not lines (strokes)
Fill the shapes with white. With all the while shapes selected, choose Object > Compound Path> Make (COMMAND + 8). This will make all the shapes act as one shape, also important for use with the pathfinder.
Select the "lines" and the test tube body and in the Pathfinder Panel, choose the Minus Front function. This will remove the "lines" from the body. If you didn't make them a compound path, all the lines but one will disappear.
Select the top line and choose Object > Path > Outline Stroke. Select both the top "line" and the body then choose the Unite Function in the Pathfinder Panel.
This will create a single object, which is necessary to do the next steps.
Draw 3 circles at the top of the test tube. One needs to be over lapping the main object.
Select JUST the circle that overlaps the main body of the test tube AND the test tube and choose the Exclude Overlap mode in the Pathfinder Panel.
This knocks out the circle where it overlaps the main body.