Unit Testing a method with a large string

Question

I'm currently using C#, but I believe the question applies to more languages.

I have a method, which takes a string value, and throws an exception, if it's too big. I want to unit test it that the exception is correct.

int vlen = Encoding.UTF8.GetByteCount(value);
if (vlen < 0 || 0x0FFFFFFF < vlen)
   throw new ArgumentException("Valid UTF8 encodded value length is up to 256MB!", "value");

What is the best way to generate such a string? Should I just have a file of that size? Should I create such a file every time running unit tests?

You can generate a string using a loop, stringbuilder, or array. — SLaks
– SLaks, Commented Feb 25, 2019 at 15:45
Consider using a stream and a stream reader, instead of having the whole string in memory. — Martin Staufcik
– Martin Staufcik, Commented Feb 25, 2019 at 15:48
@RufusL I am not sure, it isn't my code originally. I don't see how it could return a negative value here. — DisplayMyName
– DisplayMyName, Commented Feb 25, 2019 at 17:11

D Stanley · Accepted Answer · 2019-02-25 16:37:42Z

7

string has a constructor that lest you specify a length and a characer to repeat:

string longString = new string('a',0x0FFFFFFF + 1);

answered Feb 25, 2019 at 16:37

D Stanley

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Comments

René Vogt · Accepted Answer · 2019-02-25 15:51:41Z

1

You can simply use a StringBuilder:

StringBuilder builder = new StringBuilder();
builder.Append('a', 0x10000000);
string s = builder.ToString();

//Console.WriteLine(s.Length);

YourMethodToTest(s);

This takes no measurable time at my machine and I'm sure there won't be a serious performance issue on your machine either.

answered Feb 25, 2019 at 15:51

René Vogt

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Comments

Jamie Rees · Accepted Answer · 2019-02-25 15:47:11Z

0

What I would usually use in Unit Tests is a package called AutoFixture.

With that you can do the following to generate a large string:

string.Join(string.Empty, Fixture.CreateMany<char>(length))

answered Feb 25, 2019 at 15:47

Jamie Rees

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