"asdf","asdf"
"", "asdf"
"asdf", ""
"adsf", "", "asdf"

"asdf""asdf", "asdf"
"asdf", """asdf"""
"asdf", """"

(?m)""(?![ t]*(,|$))

(?m)       // enable multi-line matching (^ will act as the start of the line and $ will act as the end of the line (i))
""         // match two successive double quotes
(?!        // start negative look ahead
  [ t]*   //   zero or more spaces or tabs
  (        //   open group 1
    ,      //     match a comma
    |      //     OR
    $      //     the end of the line or string
  )        //   close group 1
)          // stop negative look ahead

orgTexts = [
    '"asdf","asdf"',
    '"", "asdf"',
    '"asdf", ""',
    '"adsf", "", "asdf"',
    '"asdf""asdf", "asdf"',
    '"asdf", """asdf"""',
    '"asdf", """"'
]

orgTexts.each{|orgText|
    # Preprocessing - Eliminate spaces before and after comma
    # Here is needed if you may have spaces before and after a valid comma
    orgText = orgText.gsub(Regexp.new('" *, *"'), '","')

    # Detect valid character (non-quote and valid quote)
    resText = orgText.gsub(Regexp.new('([^"]|^"|"$|(?<=,)"|"(?=,)|(?<=\\)")'), '-')
    # resText = orgText.gsub(Regexp.new('([^"]|(^|(?<=,)|(?<=\\))"|"($|(?=,)))'), '-')
    # [^"]       ===> A non qoute
    # |           ===> or
    # ^"         ===> beginning quot
    # |           ===> or
    # "$         ===> endding quot
    # |           ===> or
    # (?<=,)"    ===> quot just after comma
    # "(?=,)     ===> quot just before comma
    # (?<=\\)" ===> escaped quot

    #  This part is to show the invalid non-escaped quots
    print orgText
    print resText.gsub(Regexp.new('"'), '^')

    # This part is to determine if there is non-escaped quotes
    # Here is the actual matching, use this one if you don't want to know which quote is un-escaped
    isMatch = ((orgText =~ /^([^"]|^"|"$|(?<=,)"|"(?=,)|(?<=\\)")*$/) != 0).to_s
    # Basicall, it match it from start to end (^...$) there is only a valid character

    print orgText + ": " + isMatch
    print
    print ""
    print ""
}

"asdf","asdf"
-------------
"asdf","asdf": false


"","asdf"
---------
"","asdf": false


"asdf",""
---------
"asdf","": false


"adsf","","asdf"
----------------
"adsf","","asdf": false


"asdf""asdf","asdf"
-----^^------------
"asdf""asdf","asdf": true


"asdf","""asdf"""
--------^^----^^-
"asdf","""asdf""": true


"asdf",""""
--------^^-
"asdf","""": true

".*"(n|(".*",)*)

^("[^"]*"s*,s*)*"[^"]*""[^"]*"

(^|rn)("[^rn"]*"s*,s*)*"[^rn"]*""[^rn"]*"

"(?:[^",\]*|\.)*(?:""(?:[^",\]*|\.)*)+"

:%s/v("(,)@!)&(,@<!")&("(n)@!)&(^@<!")//gc

: - start the vim command
    % - scope of the command is the whole file
    s - search and replace
        / - start of search pattern
        v - simple regex syntax (rather than vim style)
            (
                " - double quote
                (,) - comma
                @! - not followed by
            )
            & - and
            (
                , - comma
                @<!- does not precedes
                " - double quote
            )
            & - and
            (
                " - double quote
                (n) - line end
                @! - not followed by
            )
            & - and
            (
                ^ - line beginning
                @<! - does not precedes
                " - double quote
            )
        / - end of search pattern and start of replace pattern
             - replace with nothing (delete)
        / - end of replace pattern
    g - apply to all the matches
    c - confirm with user for every replacement