Define 3-arg Base.show for text/plain MIME only (#29)

src/PhysicalConstants.jl

@@ -71,7 +71,7 @@ function _constant_end(qname, ename, qsym, descr, val, reference, eunit)
         Unitful.unit(::PhysicalConstant{_name($ename),T,D,U}) where {T,D,U}      = $eunit
         Unitful.dimension(::PhysicalConstant{_name($ename),T,D,U}) where {T,D,U} = D
 
-        function Base.show(io::IO, x::PhysicalConstant{_name($ename),T,D,U}) where {T,D,U}
+        function Base.show(io::IO, ::MIME"text/plain", x::PhysicalConstant{_name($ename),T,D,U}) where {T,D,U}
             unc = uncertainty(ustrip(measurement($ename)))
             println(io, $descr, " (", $qsym, ")")
             println(io, "Value                         = ", float($ename))

test/runtests.jl

@@ -47,24 +47,29 @@ end
 end
 
 @testset "Show" begin
+    function plain_repr(x)
+        io = IOBuffer()
+        show(io, "text/plain", x)
+        return String(take!(io))
+    end
     @test occursin(r"Speed of light in vacuum \(c_0\)
 Value                         = 2.99792458e8 m .*
 Standard uncertainty          = \(exact\)
 Relative standard uncertainty = \(exact\)
-Reference                     = CODATA 2014", repr(c_0))
-    @test repr(α) ==
+Reference                     = CODATA 2014", plain_repr(c_0))
+    @test plain_repr(α) ==
         "Fine-structure constant (α)
 Value                         = 0.0072973525664
 Standard uncertainty          = 1.7e-12
 Relative standard uncertainty = 2.3e-10
 Reference                     = CODATA 2014"
-    @test repr(e) ==
+    @test plain_repr(e) ==
         "Elementary charge (e)
 Value                         = 1.6021766208e-19 C
 Standard uncertainty          = 9.8e-28 C
 Relative standard uncertainty = 6.1e-9
 Reference                     = CODATA 2014"
-    @test repr(ħ) ==
+    @test plain_repr(ħ) ==
         "Planck constant over 2pi (ħ)
 Value                         = 1.0545718001391127e-34 J s
 Standard uncertainty          = 1.2891550390443523e-42 J s