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 This can help to avoid documentation examples from becoming outdated, incorrect, or misleading.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.

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
[...]

```

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.

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. It could also be that several separate doctests require the same definitions. For both of these cases a @meta block containing a DocTestSetup = ... value can be used as follows:

```jldoctest
julia> using DataFrames

julia> df = DataFrame(A = 1:10, B = 2:2:20);

```

Some text discussing `df`...

```@meta
DocTestSetup = quote
    using DataFrames
    df = DataFrame(A = 1:10, B = 2:2:20)
end
```

```jldoctest
julia> df[1, 1]
1
```

Some more text...

```jldoctest
julia> df[1, :]
1x2 DataFrames.DataFrame
| Row | A | B |
|-----|---|---|
| 1   | 1 | 2 |
```

```@meta
DocTestSetup = nothing
```

Note that the DocTestSetup value is re-evaluated at the start of each doctest block and no state is shared between any code blocks. The DocTestSetup = nothing is not strictly necessary, but good practice nonetheless to help avoid unintentional definitions later on a page.