Sample PIC source

at.pic

#
# See https://pikchr.org/home/doc/trunk/doc/userman.md
# And https://pikchr.org/home/pikchrshow
#
U:      ellipse "Unit" mono "tests" mono thickness 0 fill lightgreen 
        move wid 0.2
SHELL:  circle wid 200% thickness 0 fill lightblue
        move wid 0.2
A:      ellipse \
          "Acceptance" mono "tests" mono \
          thickness 0 fill lightblue
CORE:   circle at SHELL.c "Core" mono "logic" mono thickness 0 fill lightgreen
        arrow thin from U.e to CORE.w
        arrow thin from A.w to SHELL.e
        text "Shell" mono at SHELL.s.x,SHELL.s.y+0.1