Xref in docs and more tests for SecretBuffer (JuliaLang#29942)

base/secretbuffer.jl

@@ -3,7 +3,7 @@
 """
     Base.SecretBuffer()
 
-An IOBuffer-like object where the contents will be securely wiped when garbage collected.
+An [`IOBuffer`](@ref)-like object where the contents will be securely wiped when garbage collected.
 
 It is considered best practice to wipe the buffer using `Base.shred!(::SecretBuffer)` as
 soon as the secure data are no longer required. When initializing with existing data, the
@@ -48,7 +48,7 @@ A convenience constructor to initialize a `SecretBuffer` from a non-secret strin
 Strings are bad at keeping secrets because they are unable to be securely
 zeroed or destroyed. Therefore, avoid using this constructor with secret data.
 Instead of starting with a string, either construct the `SecretBuffer`
-incrementally with `SecretBuffer()` and `write`, or use a `Vector{UInt8}` with
+incrementally with `SecretBuffer()` and [`write`](@ref), or use a `Vector{UInt8}` with
 the `Base.SecretBuffer!(::Vector{UInt8})` constructor.
 """
 SecretBuffer(str::AbstractString) = SecretBuffer(String(str))

test/secretbuffer.jl

@@ -46,6 +46,18 @@ using Test
         @test Base.unsafe_string(ptr3) == ""
         @test s1 == s2 == s3
 
-        shred!(s1); shred!(s2); shred!(s3)
+        s4 = SecretBuffer(split("setec astronomy", " ")[1]) # initialize from SubString
+        s5 = convert(SecretBuffer, split("setec astronomy", " ")[1]) # initialize from SubString
+        @test s4 == s5
+        shred!(s1); shred!(s2); shred!(s3); shred!(s4), shred!(s5);
+    end
+    @testset "basics" begin
+        s1 = SecretBuffer("setec astronomy")
+        @test sprint(show, s1) == "SecretBuffer(\"*******\")"
+        @test !isempty(s1)
+        shred!(s1)
+        s2 = SecretBuffer!([0x00])
+        @test_throws ArgumentError Base.cconvert(Cstring, s2)
+        shred!(s2)
     end
 end