Code:
sysuse auto
regress price weight
test _b[weight]=0
mat b = e(b)
local constant : display %4.3f = b[1,2]
display `constant'
local x : display %4.3f = b[1,1]
local r2 : display %5.4f = e(r2)
local hats : display _skip(1) "̂" _skip(26) "̂"
local heads_a "y="
local heads_b "x"
local p_value : display %5.4f = r(p)
twoway (scatter price weight) || ///
(lfit price weight, ///
caption("{subscript:`hats'}" "{superscript:`heads_a' `constant'+}{superscript:`x'`heads_b'+ε }" ///
"{superscript:R-squred=`r2'}" ///
"{superscript:P-value (x-hat): `p_value'}", justification(left) position(3)) legend(off)) ///
