add filesystem tests to increase coverage (#34831)

Author: birm

Diff for: test/filesystem.jl

@@ -0,0 +1,35 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+mktempdir() do dir
+
+  # Create test file
+  filename = joinpath(dir, "file.txt")
+  text = "123456"
+  write(filename, text)
+
+  # test filesystem truncate (shorten)
+  file = Base.Filesystem.open(filename, Base.Filesystem.JL_O_RDWR)
+  Base.Filesystem.truncate(file, 2)
+  @test length(read(file)) == 2
+  close(file)
+
+  # test filesystem truncate (lengthen)
+  file = Base.Filesystem.open(filename, Base.Filesystem.JL_O_RDWR)
+  Base.Filesystem.truncate(file, 20)
+  @test length(read(file)) == 20
+  close(file)
+
+  # test filesystem futime
+  file = Base.Filesystem.open(filename, Base.Filesystem.JL_O_RDWR)
+  Base.Filesystem.futime(file, 1.0, 2.0)
+  @test Base.Filesystem.stat(file).mtime == 2.0
+  close(file)
+
+  # test filesystem readbytes!
+  file = Base.Filesystem.open(filename, Base.Filesystem.JL_O_RDWR)
+  res = ones(UInt8, 80)
+  Base.Filesystem.readbytes!(file, res)
+  @test res == UInt8[text..., (i > 20 for i in (length(text) + 1):length(res))...]
+  close(file)
+
+end