<s>
In	O
computing	O
,	O
software	B-General_Concept
engineering	I-General_Concept
,	O
and	O
software	O
testing	O
,	O
a	O
test	B-Application
oracle	I-Application
(	O
or	O
just	O
oracle	B-Application
)	O
is	O
a	O
mechanism	O
for	O
determining	O
whether	O
a	O
test	O
has	O
passed	O
or	O
failed	O
.	O
</s>
<s>
The	O
use	O
of	O
oracles	B-Application
involves	O
comparing	O
the	O
output(s )	O
of	O
the	O
system	O
under	O
test	O
,	O
for	O
a	O
given	O
test-case	O
input	O
,	O
to	O
the	O
output(s )	O
that	O
the	O
oracle	B-Application
determines	O
that	O
product	O
should	O
have	O
.	O
</s>
<s>
The	O
term	O
"	O
test	B-Application
oracle	I-Application
"	O
was	O
first	O
introduced	O
in	O
a	O
paper	O
by	O
William	O
E	O
.	O
Howden	O
.	O
</s>
<s>
Additional	O
work	O
on	O
different	O
kinds	O
of	O
oracles	B-Application
was	O
explored	O
by	O
Elaine	O
Weyuker	O
.	O
</s>
<s>
Oracles	B-Application
often	O
operate	O
separately	O
from	O
the	O
system	O
under	O
test	O
.	O
</s>
<s>
However	O
,	O
method	B-Language
postconditions	O
are	O
part	O
of	O
the	O
system	O
under	O
test	O
,	O
as	O
automated	O
oracles	B-Application
in	O
design	B-Application
by	I-Application
contract	I-Application
models	O
.	O
</s>
<s>
Determining	O
the	O
correct	O
output	O
for	O
a	O
given	O
input	O
(	O
and	O
a	O
set	O
of	O
program	O
or	O
system	O
states	O
)	O
is	O
known	O
as	O
the	O
oracle	B-Application
problem	I-Application
or	O
test	B-Application
oracle	B-Application
problem	I-Application
,	O
which	O
is	O
a	O
much	O
harder	O
problem	O
than	O
it	O
seems	O
,	O
and	O
involves	O
working	O
with	O
problems	O
related	O
to	O
controllability	O
and	O
observability	O
.	O
</s>
<s>
A	O
research	O
literature	O
survey	O
covering	O
1978	O
to	O
2012	O
found	O
several	O
potential	O
categories	O
of	O
test	B-Application
oracles	I-Application
.	O
</s>
<s>
These	O
oracles	B-Application
are	O
typically	O
associated	O
with	O
formalized	O
approaches	O
to	O
software	O
modeling	O
and	O
software	O
code	O
construction	O
.	O
</s>
<s>
They	O
are	O
connected	O
to	O
formal	B-Application
specification	I-Application
,	O
model-based	O
design	O
which	O
may	O
be	O
used	O
to	O
generate	O
test	B-Application
oracles	I-Application
,	O
state	O
transition	O
specification	B-Application
for	O
which	O
oracles	B-Application
can	O
be	O
derived	O
to	O
aid	O
model-based	O
testing	O
and	O
protocol	O
conformance	O
testing	O
,	O
and	O
design	B-Application
by	I-Application
contract	I-Application
for	O
which	O
the	O
equivalent	O
test	B-Application
oracle	I-Application
is	O
an	O
assertion	O
.	O
</s>
<s>
Specified	O
Test	B-Application
Oracles	I-Application
have	O
a	O
number	O
of	O
challenges	O
.	O
</s>
<s>
Formal	B-Application
specification	I-Application
relies	O
on	O
abstraction	O
,	O
which	O
in	O
turn	O
may	O
naturally	O
have	O
an	O
element	O
of	O
imprecision	O
as	O
all	O
models	O
cannot	O
capture	O
all	O
behavior	O
.	O
</s>
<s>
A	O
derived	O
test	B-Application
oracle	I-Application
differentiates	O
correct	O
and	O
incorrect	O
behavior	O
by	O
using	O
information	O
derived	O
from	O
artifacts	O
of	O
the	O
system	O
.	O
</s>
<s>
Regression	O
test	O
suites	O
(	O
or	O
reports	O
)	O
are	O
an	O
example	O
of	O
a	O
derived	O
test	B-Application
oracle	I-Application
-	O
they	O
are	O
built	O
on	O
the	O
assumption	O
that	O
the	O
result	O
from	O
a	O
previous	O
system	O
version	O
can	O
be	O
used	O
as	O
aid	O
(	O
oracle	B-Application
)	O
for	O
a	O
future	O
system	O
version	O
.	O
</s>
<s>
Previously	O
measured	O
performance	O
characteristics	O
may	O
be	O
used	O
as	O
an	O
oracle	B-Application
for	O
future	O
system	O
versions	O
,	O
for	O
example	O
,	O
to	O
trigger	O
a	O
question	O
about	O
observed	O
potential	O
performance	O
degradation	O
.	O
</s>
<s>
A	O
pseudo-oracle	O
falls	O
into	O
the	O
category	O
of	O
derived	O
test	B-Application
oracle	I-Application
.	O
</s>
<s>
A	O
pseudo-oracle	O
,	O
as	O
defined	O
by	O
Weyuker	O
,	O
is	O
a	O
separately	O
written	O
program	O
which	O
can	O
take	O
the	O
same	O
input	O
as	O
the	O
program	O
or	O
system	O
under	O
test	O
so	O
that	O
their	O
outputs	O
may	O
be	O
compared	O
to	O
understand	O
if	O
there	O
might	O
be	O
a	O
problem	O
to	O
investigate	O
.	O
</s>
<s>
A	O
partial	O
oracle	B-Application
is	O
a	O
hybrid	O
between	O
specified	O
test	B-Application
oracle	I-Application
and	O
derived	O
test	B-Application
oracle	I-Application
.	O
</s>
<s>
An	O
implicit	O
test	B-Application
oracle	I-Application
relies	O
on	O
implied	O
information	O
and	O
assumptions	O
.	O
</s>
<s>
unwanted	O
behavior	O
-	O
an	O
oracle	B-Application
to	O
determine	O
that	O
there	O
may	O
be	O
a	O
problem	O
.	O
</s>
<s>
There	O
are	O
limitations	O
in	O
implicit	O
test	B-Application
oracles	I-Application
-	O
as	O
they	O
rely	O
on	O
implied	O
conclusions	O
and	O
assumptions	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
program	O
or	O
process	O
crash	O
may	O
not	O
be	O
a	O
priority	O
issue	O
if	O
the	O
system	O
is	O
a	O
fault-tolerant	O
system	O
and	O
so	O
operating	O
under	O
a	O
form	O
of	O
self-healing/self	O
-management	O
.	O
</s>
<s>
Implicit	O
test	B-Application
oracles	I-Application
may	O
be	O
susceptible	O
to	O
false	O
positives	O
due	O
to	O
environment	O
dependencies	O
.	O
</s>
<s>
Property	O
based	O
testing	O
relies	O
on	O
implicit	O
oracles	B-Application
.	O
</s>
<s>
When	O
specified	O
,	O
derived	O
or	O
implicit	O
test	B-Application
oracles	I-Application
cannot	O
be	O
used	O
,	O
then	O
human	O
input	O
to	O
determine	O
the	O
test	B-Application
oracles	I-Application
is	O
required	O
.	O
</s>
<s>
These	O
can	O
be	O
guided	O
by	O
heuristic	B-Algorithm
approaches	O
,	O
such	O
as	O
gut	O
instincts	O
,	O
rules	O
of	O
thumb	O
,	O
checklist	O
aids	O
,	O
and	O
experience	O
to	O
help	O
tailor	O
the	O
specific	O
combination	O
selected	O
for	O
the	O
program/system	O
under	O
test	O
.	O
</s>
<s>
Test	B-Application
oracles	I-Application
are	O
most	O
commonly	O
based	O
on	O
specifications	B-Application
and	O
documentation	O
.	O
</s>
<s>
A	O
formal	B-Application
specification	I-Application
used	O
as	O
input	O
to	O
model-based	O
design	O
and	O
model-based	O
testing	O
would	O
be	O
an	O
example	O
of	O
a	O
specified	O
test	B-Application
oracle	I-Application
.	O
</s>
<s>
The	O
model-based	O
oracle	B-Application
uses	O
the	O
same	O
model	O
to	O
generate	O
and	O
verify	O
system	O
behavior	O
.	O
</s>
<s>
Documentation	O
that	O
is	O
not	O
a	O
full	O
specification	B-Application
of	O
the	O
product	O
,	O
such	O
as	O
a	O
usage	O
or	O
installation	O
guide	O
,	O
or	O
a	O
record	O
of	O
performance	O
characteristics	O
or	O
minimum	O
machine	O
requirements	O
for	O
the	O
software	O
,	O
would	O
typically	O
be	O
a	O
derived	O
test	B-Application
oracle	I-Application
.	O
</s>
<s>
A	O
consistency	O
oracle	B-Application
compares	O
the	O
results	O
of	O
one	O
test	O
execution	O
to	O
another	O
for	O
similarity	O
.	O
</s>
<s>
This	O
is	O
another	O
example	O
of	O
a	O
derived	O
test	B-Application
oracle	I-Application
.	O
</s>
<s>
An	O
oracle	B-Application
for	O
a	O
software	O
program	O
might	O
be	O
a	O
second	O
program	O
that	O
uses	O
a	O
different	O
algorithm	O
to	O
evaluate	O
the	O
same	O
mathematical	O
expression	O
as	O
the	O
product	O
under	O
test	O
.	O
</s>
<s>
This	O
is	O
an	O
example	O
of	O
a	O
pseudo-oracle	O
,	O
which	O
is	O
a	O
derived	O
test	B-Application
oracle	I-Application
.	O
</s>
<s>
During	O
Google	B-Application
search	O
,	O
we	O
do	O
not	O
have	O
a	O
complete	O
oracle	B-Application
to	O
verify	O
whether	O
the	O
number	O
of	O
returned	O
results	O
is	O
correct	O
.	O
</s>
<s>
This	O
is	O
an	O
example	O
of	O
a	O
partial	O
oracle	B-Application
,	O
which	O
is	O
a	O
hybrid	O
between	O
specified	O
test	B-Application
oracle	I-Application
and	O
derived	O
test	B-Application
oracle	I-Application
.	O
</s>
<s>
A	O
statistical	O
oracle	B-Application
uses	O
probabilistic	O
characteristics	O
,	O
for	O
example	O
with	O
image	O
analysis	O
where	O
a	O
range	O
of	O
certainty	O
and	O
uncertainty	O
is	O
defined	O
for	O
the	O
test	B-Application
oracle	I-Application
to	O
pronounce	O
a	O
match	O
or	O
otherwise	O
.	O
</s>
<s>
This	O
would	O
be	O
an	O
example	O
of	O
a	O
quantitative	O
approach	O
in	O
human	O
test	B-Application
oracle	I-Application
.	O
</s>
<s>
A	O
heuristic	B-Algorithm
oracle	B-Application
provides	O
representative	O
or	O
approximate	O
results	O
over	O
a	O
class	O
of	O
test	O
inputs	O
.	O
</s>
<s>
This	O
would	O
be	O
an	O
example	O
of	O
a	O
qualitative	O
approach	O
in	O
human	O
test	B-Application
oracle	I-Application
.	O
</s>
