Create diagnostics.jl

Author: DilumAluthge

stdlib/LinearAlgebra/test/diagnostics.jl

@@ -0,0 +1,9 @@
+@testset "__diagnostics__()" begin
+    # check that `LinearAlgebra.__diagnostics__(io)` doesn't error, produces some output
+    buf = PipeBuffer()
+    LinearAlgebra.__diagnostics__(buf)
+    output = read(buf, String)
+    @test !isempty(strip(output))
+
+    NetworkOptions.__diagnostics__(stdout) # TODO: delete this line before merging the PR
+end