RUBY-1595 Improve error reporting when symbol/string is passed as read preference (#2582)

* RUBY-1595 Improve error reporting when symbol/string is passed as read preference

* tweak wording

* RUBY-1595 fix tests

Co-authored-by: Oleg Pudeyev <code@olegp.name>

Author: neilshweky

lib/mongo/client.rb

@@ -1570,7 +1570,7 @@ def validate_read!(option, opts)
         # for custom classes implementing key access ([]).
         # Instead reject common cases of strings and symbols.
         if read.is_a?(String) || read.is_a?(Symbol)
-          raise Error::InvalidReadOption.new(read, 'must be a hash')
+          raise Error::InvalidReadOption.new(read, "the read preference must be specified as a hash: { mode: #{read.inspect} }")
         end
 
         if mode = read[:mode]

lib/mongo/error/invalid_read_option.rb

@@ -31,7 +31,7 @@ class InvalidReadOption < Error
       #
       # @since 2.6.0
       def initialize(read_option, msg)
-        super("Invalid read option: #{read_option}: #{msg}")
+        super("Invalid read preference value: #{read_option.inspect}: #{msg}")
       end
     end
   end

spec/mongo/client_construction_spec.rb

@@ -1773,28 +1773,28 @@
             expect do
               client = new_local_client_nmio(['127.0.0.1:27017'],
                 :read => {:mode => :bogus})
-            end.to raise_error(Mongo::Error::InvalidReadOption, 'Invalid read option: {"mode"=>:bogus}: mode bogus is not one of recognized modes')
+            end.to raise_error(Mongo::Error::InvalidReadOption, 'Invalid read preference value: {"mode"=>:bogus}: mode bogus is not one of recognized modes')
           end
 
           it 'rejects bogus read preference as string' do
             expect do
               client = new_local_client_nmio(['127.0.0.1:27017'],
                 :read => {:mode => 'bogus'})
-            end.to raise_error(Mongo::Error::InvalidReadOption, 'Invalid read option: {"mode"=>"bogus"}: mode bogus is not one of recognized modes')
+            end.to raise_error(Mongo::Error::InvalidReadOption, 'Invalid read preference value: {"mode"=>"bogus"}: mode bogus is not one of recognized modes')
           end
 
           it 'rejects read option specified as a string' do
             expect do
               client = new_local_client_nmio(['127.0.0.1:27017'],
                 :read => 'primary')
-            end.to raise_error(Mongo::Error::InvalidReadOption, 'Invalid read option: primary: must be a hash')
+            end.to raise_error(Mongo::Error::InvalidReadOption, 'Invalid read preference value: "primary": the read preference must be specified as a hash: { mode: "primary" }')
           end
 
           it 'rejects read option specified as a symbol' do
             expect do
               client = new_local_client_nmio(['127.0.0.1:27017'],
                 :read => :primary)
-            end.to raise_error(Mongo::Error::InvalidReadOption, 'Invalid read option: primary: must be a hash')
+            end.to raise_error(Mongo::Error::InvalidReadOption, "Invalid read preference value: :primary: the read preference must be specified as a hash: { mode: :primary }")
           end
         end
       end