Doctests

Documenter will, by default, try to run jldoctest code blocks that it finds in the generated documentation. This can help to avoid documentation examples from becoming outdated, incorrect, or misleading. It's recommended that as many of a package's examples be runnable by Documenter's doctest.

This section of the manual outlines how to go about enabling doctests for code blocks in your package's documentation.

"Script" Examples

The first, of two, types of doctests is the "script" code block. To make Documenter detect this kind of code block the following format must be used:

```jldoctest
a = 1
b = 2
a + b

# output

3
```

The code block's "language" must be jldoctest and must include a line containing the text # output. The text before this line is the contents of the script which is run. The text that appears after # output is the textual representation that would be shown in the Julia REPL if the script had been included.

The actual output produced by running the "script" is compared to the expected result and any difference will result in makedocs throwing an error and terminating.

Note that the amount of whitespace appearing above and below the # output line is not significant and can be increased or decreased if desired.

It is possible to suppress the output from the doctest by setting the output keyword argument to false, for example

```jldoctest; output = false
a = 1
b = 2
a + b

# output

3
```

Note that the output of the script will still be compared to the expected result, i.e. what is # output section, but the # output section will be suppressed in the rendered documentation.

REPL Examples

The other kind of doctest is a simulated Julia REPL session. The following format is detected by Documenter as a REPL doctest:

```jldoctest
julia> a = 1
1

julia> b = 2;

julia> c = 3;  # comment

julia> a + b + c
6
```

As with script doctests, the code block must have it's language set to jldoctest. When a code block contains one or more julia> at the start of a line then it is assumed to be a REPL doctest. Semi-colons, ;, at the end of a line works in the same way as in the Julia REPL and will suppress the output, although the line is still evaluated.

Note that not all features of the REPL are supported such as shell and help modes.

Exceptions

Doctests can also test for thrown exceptions and their stacktraces. Comparing of the actual and expected results is done by checking whether the expected result matches the start of the actual result. Hence, both of the following errors will match the actual result.

```jldoctest
julia> div(1, 0)
ERROR: DivideError: integer division error
 in div(::Int64, ::Int64) at ./int.jl:115

julia> div(1, 0)
ERROR: DivideError: integer division error
```

If instead the first div(1, 0) error was written as

```jldoctest
julia> div(1, 0)
ERROR: DivideError: integer division error
 in div(::Int64, ::Int64) at ./int.jl:114
```

where line 115 is replaced with 114 then the doctest will fail.

In the second div(1, 0), where no stacktrace is shown, it may appear to the reader that it is expected that no stacktrace will actually be displayed when they attempt to try to recreate the error themselves. To indicate to readers that the output result is truncated and does not display the entire (or any of) the stacktrace you may write [...] at the line where checking should stop, i.e.

```jldoctest
julia> div(1, 0)
ERROR: DivideError: integer division error
[...]
```

Preserving Definitions Between Blocks

Every doctest block is evaluated inside its own module. This means that definitions (types, variables, functions etc.) from a block can not be used in the next block. For example:

```jldoctest
julia> foo = 42
42
```

The variable foo will not be defined in the next block:

```jldoctest
julia> println(foo)
ERROR: UndefVarError: foo not defined
```

To preserve definitions it is possible to label blocks in order to collect several blocks into the same module. All blocks with the same label (in the same file) will be evaluated in the same module, and hence share scope. This can be useful if the same definitions are used in more than one block, with for example text, or other doctest blocks, in between. Example:

```jldoctest mylabel
julia> foo = 42
42
```

Now, since the block below has the same label as the block above, the variable foo can be used:

```jldoctest mylabel
julia> println(foo)
42
```

Setup Code

Doctests may require some setup code that must be evaluated prior to that of the actual example, but that should not be displayed in the final documentation. For this purpose a @meta block containing a DocTestSetup = ... value can be used. In the example below, the function foo is defined inside a @meta block. This block will be evaluated at the start of the following doctest blocks:

```@meta
DocTestSetup = quote
    function foo(x)
        return x^2
    end
end
```

```jldoctest
julia> foo(2)
4
```

```@meta
DocTestSetup = nothing
```

The DocTestSetup = nothing is not strictly necessary, but good practice nonetheless to help avoid unintentional definitions in following doctest blocks.

Another option is to use the setup keyword argument, which is convenient for short definitions, and for setups needed in inline docstrings.

```jldoctest; setup = :(foo(x) = x^2)
julia> foo(2)
4
```

Filtering Doctests

A part of the output of a doctest might be non-deterministic, e.g. pointer addresses and timings. It is therefore possible to filter a doctest so that the deterministic part can still be tested.

A filter takes the form of a regular expression. In a doctest, each match in the expected output and the actual output is removed before the two outputs are compared. Filters are added globally, i.e. applied to all doctests in the documentation, by passing a list of regular expressions to makedocs with the keyword doctestfilters.

For more fine grained control it is possible to define filters in @meta blocks by assigning them to the DocTestFilters variable, either as a single regular expression (DocTestFilters = [r"foo"]) or as a vector of several regex (DocTestFilters = [r"foo", r"bar"]).

An example is given below where some of the non-deterministic output from @time is filtered.

```@meta
DocTestFilters = r"[0-9\.]+ seconds \(.*\)"
```

```jldoctest
julia> @time [1,2,3,4]
  0.000003 seconds (5 allocations: 272 bytes)
4-element Array{Int64,1}:
 1
 2
 3
 4
```

```@meta
DocTestFilters = nothing
```

The DocTestFilters = nothing is not strictly necessary, but good practice nonetheless to help avoid unintentional filtering in following doctest blocks.

Another option is to use the filter keyword argument. This defines a doctest-local filter which is only active for the specific doctest. Note that such filters are not shared between named doctests either. It is possible to define a filter by a single regex (filter = r"foo") or as a list of regex (filter = [r"foo", r"bar"]). Example:

```jldoctest; filter = r"[0-9\.]+ seconds \(.*\)"
julia> @time [1,2,3,4]
  0.000003 seconds (5 allocations: 272 bytes)
4-element Array{Int64,1}:
 1
 2
 3
 4
```

Fixing Outdated Doctests

To fix outdated doctests, the doctest flag to makedocs can be set to doctest = :fix. This will run the doctests, and overwrite the old results with the new output.

Skipping Doctests

Doctesting can be disabled by setting the makedocs keyword doctest = false. This should only be done when initially laying out the structure of a package's documentation, after which it's encouraged to always run doctests when building docs.