<s>
Selenium	B-Library
is	O
an	O
open	B-License
source	I-License
umbrella	O
project	O
for	O
a	O
range	O
of	O
tools	O
and	O
libraries	O
aimed	O
at	O
supporting	O
browser	B-Protocol
automation	I-Protocol
.	O
</s>
<s>
It	O
provides	O
a	O
playback	O
tool	O
for	O
authoring	O
functional	B-Application
tests	I-Application
across	O
most	O
modern	O
web	B-Application
browsers	I-Application
,	O
without	O
the	O
need	O
to	O
learn	O
a	O
test	O
scripting	B-Language
language	I-Language
(	O
Selenium	B-Library
IDE	I-Library
)	O
.	O
</s>
<s>
It	O
also	O
provides	O
a	O
test	O
domain-specific	B-Language
language	I-Language
(	O
Selenese	B-Library
)	O
to	O
write	O
tests	O
in	O
a	O
number	O
of	O
popular	O
programming	O
languages	O
,	O
including	O
JavaScript	B-Language
(	O
Node.js	B-Language
)	O
,	O
C#	B-Application
,	O
Groovy	B-Application
,	O
Java	B-Language
,	O
Perl	B-Language
,	O
PHP	B-Application
,	O
Python	B-Language
,	O
Ruby	B-Language
and	O
Scala	B-Application
.	O
</s>
<s>
Selenium	B-Library
runs	O
on	O
Windows	B-Application
,	O
Linux	B-Application
,	O
and	O
macOS	B-Application
.	O
</s>
<s>
It	O
is	O
open-source	B-Application
software	I-Application
released	O
under	O
the	O
Apache	B-Application
License	I-Application
2.0	I-Application
.	O
</s>
<s>
Selenium	B-Library
was	O
originally	O
developed	O
by	O
Jason	O
Huggins	O
in	O
2004	O
as	O
an	O
internal	O
tool	O
at	O
ThoughtWorks	B-Application
.	O
</s>
<s>
Huggins	O
was	O
later	O
joined	O
by	O
other	O
programmers	O
and	O
testers	O
at	O
ThoughtWorks	B-Application
,	O
before	O
Paul	O
Hammant	O
joined	O
the	O
team	O
and	O
steered	O
the	O
development	O
of	O
the	O
second	O
mode	O
of	O
operation	O
that	O
would	O
later	O
become	O
"	O
Selenium	B-Library
Remote	O
Control	O
"	O
(	O
RC	O
)	O
.	O
</s>
<s>
In	O
2005	O
Dan	O
Fabulich	O
and	O
Nelson	O
Sproul	O
(	O
with	O
help	O
from	O
Pat	O
Lightbody	O
)	O
made	O
an	O
offer	O
to	O
accept	O
a	O
series	O
of	O
patches	O
that	O
would	O
transform	O
Selenium-RC	O
into	O
what	O
it	O
became	O
best	O
known	O
for	O
.	O
</s>
<s>
In	O
the	O
same	O
meeting	O
,	O
the	O
steering	O
of	O
Selenium	B-Library
as	O
a	O
project	O
would	O
continue	O
as	O
a	O
committee	O
,	O
with	O
Huggins	O
and	O
Hammant	O
being	O
the	O
ThoughtWorks	B-Application
representatives	O
.	O
</s>
<s>
Together	O
with	O
others	O
like	O
Jennifer	O
Bevan	O
,	O
he	O
continued	O
with	O
the	O
development	O
and	O
stabilization	O
of	O
Selenium	B-Library
RC	I-Library
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
Simon	O
Stewart	O
at	O
ThoughtWorks	B-Application
developed	O
a	O
superior	O
browser	B-Protocol
automation	I-Protocol
tool	O
called	O
WebDriver	O
.	O
</s>
<s>
In	O
2009	O
,	O
after	O
a	O
meeting	O
between	O
the	O
developers	O
at	O
the	O
Google	O
Test	B-Application
Automation	I-Application
Conference	O
,	O
it	O
was	O
decided	O
to	O
merge	O
the	O
two	O
projects	O
,	O
and	O
call	O
the	O
new	O
project	O
Selenium	B-Library
WebDriver	O
,	O
or	O
Selenium	B-Library
2.0	O
.	O
</s>
<s>
In	O
2008	O
,	O
Philippe	O
Hanrigou	O
(	O
then	O
at	O
ThoughtWorks	B-Application
)	O
made	O
"	O
Selenium	B-Library
Grid	O
"	O
,	O
which	O
provides	O
a	O
hub	O
allowing	O
the	O
running	O
of	O
multiple	O
Selenium	B-Library
tests	O
concurrently	O
on	O
any	O
number	O
of	O
local	O
or	O
remote	O
systems	O
,	O
thus	O
minimizing	O
test	O
execution	O
time	O
.	O
</s>
<s>
Grid	O
offered	O
,	O
as	O
open	B-License
source	I-License
,	O
a	O
similar	O
capability	O
to	O
the	O
internal/private	O
Google	O
cloud	O
for	O
Selenium	B-Library
RC	I-Library
.	O
</s>
<s>
The	O
name	O
Selenium	B-Library
comes	O
from	O
a	O
joke	O
made	O
by	O
Huggins	O
in	O
an	O
email	O
,	O
mocking	O
a	O
competitor	O
named	O
Mercury	O
,	O
saying	O
that	O
you	O
can	O
cure	O
mercury	O
poisoning	O
by	O
taking	O
selenium	B-Library
supplements	O
.	O
</s>
<s>
Selenium	B-Library
is	O
composed	O
of	O
several	O
components	O
with	O
each	O
taking	O
on	O
a	O
specific	O
role	O
in	O
aiding	O
the	O
development	O
of	O
web	B-Application
application	I-Application
test	B-Application
automation	I-Application
.	O
</s>
<s>
Selenium	B-Library
IDE	I-Library
is	O
a	O
complete	O
integrated	B-Application
development	I-Application
environment	I-Application
(	O
IDE	O
)	O
for	O
Selenium	B-Library
tests	O
.	O
</s>
<s>
It	O
is	O
implemented	O
as	O
a	O
Firefox	B-Operating_System
Add-On	I-Operating_System
and	O
as	O
a	O
Chrome	B-Application
Extension	I-Application
.	O
</s>
<s>
It	O
allows	O
for	O
recording	O
,	O
editing	O
and	O
debugging	O
of	O
functional	B-Application
tests	I-Application
.	O
</s>
<s>
It	O
was	O
previously	O
known	O
as	O
Selenium	B-Library
Recorder	I-Library
.	O
</s>
<s>
Selenium-IDE	O
was	O
originally	O
created	O
by	O
Shinya	O
Kasatani	O
and	O
donated	O
to	O
the	O
Selenium	B-Library
project	O
in	O
2006	O
.	O
</s>
<s>
Selenium	B-Library
IDE	I-Library
began	O
being	O
actively	O
maintained	O
in	O
2018	O
.	O
</s>
<s>
Scripts	O
are	O
recorded	O
in	O
Selenese	B-Library
,	O
a	O
special	O
test	O
scripting	B-Language
language	I-Language
for	O
Selenium	B-Library
.	O
</s>
<s>
Selenese	B-Library
provides	O
commands	O
for	O
performing	O
actions	O
in	O
a	O
browser	B-Application
(	O
click	O
a	O
link	O
,	O
select	O
an	O
option	O
)	O
and	O
for	O
retrieving	O
data	O
from	O
the	O
resulting	O
pages	O
.	O
</s>
<s>
As	O
an	O
alternative	O
to	O
writing	O
tests	O
in	O
Selenese	B-Library
,	O
tests	O
can	O
also	O
be	O
written	O
in	O
various	O
programming	O
languages	O
.	O
</s>
<s>
These	O
tests	O
then	O
communicate	O
with	O
Selenium	B-Library
by	O
calling	O
methods	O
in	O
the	O
Selenium	B-Library
Client	O
API	O
.	O
</s>
<s>
Selenium	B-Library
currently	O
provides	O
client	O
APIs	O
for	O
Java	B-Language
,	O
C#	B-Application
,	O
Ruby	B-Language
,	O
JavaScript	B-Language
,	O
R	B-Language
and	O
Python	B-Language
.	O
</s>
<s>
Selenium	B-Library
Remote	O
Control	O
(	O
RC	O
)	O
is	O
a	O
server	O
,	O
written	O
in	O
Java	B-Language
,	O
that	O
accepts	O
commands	O
for	O
the	O
browser	B-Application
via	O
HTTP	B-Protocol
.	I-Protocol
</s>
<s>
RC	O
makes	O
it	O
possible	O
to	O
write	O
automated	B-Application
tests	I-Application
for	O
a	O
web	B-Application
application	I-Application
in	O
any	O
programming	O
language	O
,	O
which	O
allows	O
for	O
better	O
integration	O
of	O
Selenium	B-Library
in	O
existing	O
unit	O
test	O
frameworks	O
.	O
</s>
<s>
To	O
make	O
writing	O
tests	O
easier	O
,	O
Selenium	B-Library
project	O
currently	O
provides	O
client	O
drivers	O
for	O
PHP	B-Application
,	O
Python	B-Language
,	O
Ruby	B-Language
,	O
.NET	B-Application
,	O
Perl	B-Language
and	O
Java	B-Language
.	O
</s>
<s>
The	O
Java	B-Language
driver	O
can	O
also	O
be	O
used	O
with	O
JavaScript	B-Language
(	O
via	O
the	O
Rhino	B-Language
engine	O
)	O
.	O
</s>
<s>
An	O
instance	O
of	O
selenium	B-Library
RC	I-Library
server	O
is	O
needed	O
to	O
launch	O
html	O
test	O
case	O
-	O
which	O
means	O
that	O
the	O
port	O
should	O
be	O
different	O
for	O
each	O
parallel	O
run	O
.	O
</s>
<s>
However	O
,	O
for	O
Java/PHP	O
test	O
case	O
only	O
one	O
Selenium	B-Library
RC	I-Library
instance	O
needs	O
to	O
be	O
running	O
continuously	O
.	O
</s>
<s>
Selenium	B-Library
Remote	O
Control	O
was	O
a	O
refactoring	O
of	O
Driven	O
Selenium	B-Library
or	O
Selenium	B-Library
B	O
designed	O
by	O
Paul	O
Hammant	O
,	O
credited	O
with	O
Jason	O
as	O
co-creator	O
of	O
Selenium	B-Library
.	O
</s>
<s>
The	O
original	O
version	O
directly	O
launched	O
a	O
process	O
for	O
the	O
browser	B-Application
in	O
question	O
,	O
from	O
the	O
test	O
language	O
of	O
Java	B-Language
,	O
.NET	B-Application
,	O
Python	B-Language
or	O
Ruby	B-Language
.	O
</s>
<s>
The	O
wire	O
protocol	O
(	O
called	O
'	O
Selenese	B-Library
 '	O
in	O
its	O
day	O
)	O
was	O
reimplemented	O
in	O
each	O
language	O
port	O
.	O
</s>
<s>
After	O
the	O
refactor	O
by	O
Dan	O
Fabulich	O
and	O
Nelson	O
Sproul	O
(	O
with	O
help	O
from	O
Pat	O
Lightbody	O
)	O
there	O
was	O
an	O
intermediate	O
daemon	O
process	O
between	O
the	O
driving	O
test	O
script	O
and	O
the	O
browser	B-Application
.	O
</s>
<s>
The	O
benefits	O
included	O
the	O
ability	O
to	O
drive	O
remote	O
browsers	B-Application
and	O
the	O
reduced	O
need	O
to	O
port	O
every	O
line	O
of	O
code	O
to	O
an	O
increasingly	O
growing	O
set	O
of	O
languages	O
.	O
</s>
<s>
Selenium	B-Library
Remote	O
Control	O
completely	O
took	O
over	O
from	O
the	O
Driven	O
Selenium	B-Library
code-line	O
in	O
2006	O
.	O
</s>
<s>
The	O
browser	B-Application
pattern	O
for	O
'	O
Driven'/'B'	O
and	O
'	O
RC	O
 '	O
was	O
response/request	O
,	O
which	O
subsequently	O
became	O
known	O
as	O
Comet	B-General_Concept
.	O
</s>
<s>
Selenium	B-Library
RC	I-Library
served	O
as	O
the	O
flagship	O
testing	O
framework	B-Architecture
of	O
the	O
entire	O
project	O
of	O
selenium	B-Library
for	O
a	O
long-standing	O
time	O
.	O
</s>
<s>
And	O
significantly	O
Selenium	B-Library
RC	I-Library
is	O
the	O
first	O
and	O
foremost	O
automated	O
web	O
testing	B-Application
tool	I-Application
that	O
enabled	O
users	O
to	O
adopt	O
their	O
preferred	O
programming	O
language	O
.	O
</s>
<s>
With	O
the	O
release	O
of	O
Selenium	B-Library
2	O
,	O
Selenium	B-Library
RC	I-Library
has	O
been	O
officially	O
deprecated	O
in	O
favor	O
of	O
Selenium	B-Library
WebDriver	O
.	O
</s>
<s>
At	O
the	O
core	O
of	O
Selenium	B-Library
is	O
Selenium	B-Library
WebDriver	O
,	O
an	O
interface	O
to	O
write	O
instructions	O
that	O
work	O
interchangeably	O
across	O
browsers	B-Application
.	O
</s>
<s>
It	O
is	O
the	O
successor	O
to	O
Selenium	B-Library
RC	I-Library
.	O
</s>
<s>
Selenium	B-Library
WebDriver	O
accepts	O
commands	O
(	O
sent	O
in	O
Selenese	B-Library
,	O
or	O
via	O
a	O
Client	O
API	O
)	O
and	O
sends	O
them	O
to	O
a	O
browser	B-Application
.	O
</s>
<s>
This	O
is	O
implemented	O
through	O
a	O
browser-specific	O
browser	B-Application
driver	O
,	O
which	O
sends	O
commands	O
to	O
a	O
browser	B-Application
and	O
retrieves	O
results	O
.	O
</s>
<s>
Most	O
browser	B-Application
drivers	O
actually	O
launch	O
and	O
access	O
a	O
browser	B-Application
application	I-Application
(	O
such	O
as	O
Firefox	B-Application
,	O
Google	B-Application
Chrome	I-Application
,	O
Internet	B-Application
Explorer	I-Application
,	O
Safari	B-Application
,	O
or	O
Microsoft	B-Application
Edge	I-Application
)	O
;	O
there	O
is	O
also	O
an	O
HtmlUnit	B-Language
browser	B-Application
driver	O
,	O
which	O
simulates	O
a	O
browser	B-Application
using	O
the	O
headless	B-Protocol
browser	I-Protocol
HtmlUnit	B-Language
.	O
</s>
<s>
Unlike	O
in	O
Selenium	B-Library
1	O
,	O
where	O
the	O
Selenium	B-Library
server	O
was	O
necessary	O
to	O
run	O
tests	O
,	O
Selenium	B-Library
WebDriver	O
does	O
not	O
need	O
a	O
special	O
server	O
to	O
execute	O
tests	O
.	O
</s>
<s>
Instead	O
,	O
the	O
WebDriver	O
directly	O
starts	O
a	O
browser	B-Application
instance	O
and	O
controls	O
it	O
.	O
</s>
<s>
However	O
,	O
Selenium	B-Library
Grid	O
can	O
be	O
used	O
with	O
WebDriver	O
to	O
execute	O
tests	O
on	O
remote	O
systems	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
Where	O
possible	O
,	O
WebDriver	O
uses	O
native	O
operating	O
system	O
level	O
functionality	O
rather	O
than	O
browser-based	B-Application
JavaScript	B-Language
commands	O
to	O
drive	O
the	O
browser	B-Application
.	O
</s>
<s>
This	O
bypasses	O
problems	O
with	O
subtle	O
differences	O
between	O
native	O
and	O
JavaScript	B-Language
commands	O
,	O
including	O
security	O
restrictions	O
.	O
</s>
<s>
Selenium	B-Library
WebDriver	O
(	O
Selenium	B-Library
2.0	O
)	O
is	O
fully	O
implemented	O
and	O
supported	O
in	O
JavaScript	B-Language
(	O
Node.js	B-Language
)	O
,	O
Python	B-Language
,	O
Ruby	B-Language
,	O
Java	B-Language
,	O
Kotlin	B-Language
(	O
programming	O
language	O
)	O
,	O
and	O
C#	B-Application
.	O
</s>
<s>
As	O
of	O
2021	O
,	O
Selenium	B-Library
4	O
is	O
a	O
release	O
candidate	O
.	O
</s>
<s>
Selenium	B-Library
Grid	O
is	O
a	O
server	O
that	O
allows	O
tests	O
to	O
use	O
web	B-Application
browser	I-Application
instances	O
running	O
on	O
remote	O
machines	O
.	O
</s>
<s>
With	O
Selenium	B-Library
Grid	O
,	O
one	O
server	O
acts	O
as	O
the	O
central	O
hub	O
.	O
</s>
<s>
Tests	O
contact	O
the	O
hub	O
to	O
obtain	O
access	O
to	O
browser	B-Application
instances	O
.	O
</s>
<s>
The	O
hub	O
has	O
a	O
list	O
of	O
servers	O
that	O
provide	O
access	O
to	O
browser	B-Application
instances	O
(	O
WebDriver	O
nodes	O
)	O
,	O
and	O
lets	O
tests	O
use	O
these	O
instances	O
.	O
</s>
<s>
Selenium	B-Library
Grid	O
allows	O
running	O
tests	O
in	O
parallel	O
on	O
multiple	O
machines	O
and	O
to	O
manage	O
different	O
browser	B-Application
versions	O
and	O
browser	B-Application
configurations	O
centrally	O
(	O
instead	O
of	O
in	O
each	O
individual	O
test	O
)	O
.	O
</s>
<s>
The	O
ability	O
to	O
run	O
tests	O
on	O
remote	O
browser	B-Application
instances	O
is	O
useful	O
to	O
spread	O
the	O
load	O
of	O
testing	O
across	O
several	O
machines	O
and	O
to	O
run	O
tests	O
in	O
browsers	B-Application
running	O
on	O
different	O
platforms	O
or	O
operating	O
systems	O
.	O
</s>
<s>
The	O
latter	O
is	O
particularly	O
useful	O
in	O
cases	O
where	O
not	O
all	O
browsers	B-Application
to	O
be	O
used	O
for	O
testing	O
can	O
run	O
on	O
the	O
same	O
platform	O
.	O
</s>
