Fix tape printing (#252)

* Fix tape printing

* Update tape.jl

Co-authored-by: David Widmann <devmotion@users.noreply.github.com>

* Add string test

---------

Co-authored-by: David Widmann <devmotion@users.noreply.github.com>

Author: gdalle

src/tape.jl

@@ -110,7 +110,7 @@ function Base.show(io::IO, instruction::AbstractInstruction, pad = "")
 end
 
 function Base.show(io::IO, tp::InstructionTape)
-    println("$(length(tp))-element InstructionTape:")
+    println(io, length(tp), "-element InstructionTape:")
     i = 1
     for instruction in tp
         print(io, "$i => ")

test/TapeTests.jl

@@ -31,6 +31,7 @@ for Instr in (SpecialInstruction, ScalarInstruction)
     @test tp[1].input[2] == y
     @test tp[1].output === z
     @test tp[1].cache === c
+    @test startswith(string(tp), "1-element InstructionTape:")
 
     ReverseDiff.record!(NULL_TAPE, Instr, +, (x, y, k), z, c)
     @test isempty(NULL_TAPE)