On Tue, Jan 04, 2022 at 05:01:41PM +0000, Amit via Digitalmars-d-learn wrote:
> Hi!
>
> I wrote a text parser that takes a File argument and parses that
> file's contents. Now I would like to write a unit-test for that
> parser. I need a File (or a general IO interface) that reads from an
> in-memory buffer, similar to python's `StringIO` or go's
> `strings.Reader`.
>
> How can I achieve that?
>
> Example of what I have in mind:
>
> ```d
> unittest {
> string fakeContents = "foo\nbar\nbaz";
> File f = createFileFromString(fakeContents);
> assert(myParse(f) == MyParsedObject(...));
> }
> ```
It's very easy, just have your text parser take File as a template
argument, defaulted to std.file.File, that your unittest(s) can override
with a custom type containing the needed methods. For example:
auto myParser(File = std.stdio.File)(File input) {
... // read input as usual
}
unittest {
struct FakeFile {
string contents = "...";
void[] rawRead(void[] buf) {
... // simulate a file read here
}
... // add whatever other File methods you might need
here
}
FakeFile f;
auto output = myParser(f);
...
}
void main() {
auto input = File("...", "r");
auto output = myParser(input); // `File` defaults to
std.stdio.File
...
}
T
--
"A man's wife has more power over him than the state has." -- Ralph Emerson
