add test for .rds file format and a test file

Author: jsams

test/files/minimal_ascii.rds

@@ -0,0 +1,40 @@
+A
+2
+197634
+131840
+787
+1
+14
+2
+1.1
+2.2
+1026
+1
+262153
+5
+names
+16
+1
+262153
+3
+num
+1026
+1
+262153
+9
+row.names
+13
+2
+NA
+-2
+1026
+1
+262153
+5
+class
+16
+1
+262153
+10
+data.frame
+254

test/query.jl

@@ -319,6 +319,16 @@ end
         @test (position(io) in (5, 6))
     end
 end
+@testset "RDS detection" begin
+    q = query(joinpath(file_dir, "minimal_ascii.rds"))
+    @test typeof(q) == File{format"RDataSingle"}
+    open(q) do io
+        @test position(io) == 0
+        @test FileIO.detect_rdata_single(io)
+        # need to seek to beginning of file where data structure starts
+        @test position(io)  == 0
+    end
+end
 @testset "Format with function for magic bytes" begin
     add_format(format"FUNCTION_FOR_MAGIC_BYTES", x -> 0x00, ".wav", [:WAV])
     del_format(format"FUNCTION_FOR_MAGIC_BYTES")