The ornamental design for a portable testinstrument, as shown and described.
FIG. 1 is a top front perspective view of a portable test instrument showing the new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The portions shown in broken lines, represented as dashed lines, depict environmental structure only and do not form part of the claimed design.
The broken lines represented as dot-dash lines, crossing the article in all views, depict break lines which form no part of the claimed design. The appearance of any portion of the article between the dot-dash lines forms no part of the claimed design.