How to test db errors in go?

Question

I am implementing a storer that is backed by leveldb (https://github.com/syndtr/goleveldb) in go. I am new to go and am trying to figure out how I get test coverage for the condition in the code below where perr != nil. I can test my own errors ok, but I can't figure out how to reliably get the Put method of leveldb to return an error. Mocking out a db just to get test coverage up for a few edge cases seems like a lot of work for not much reward. Is mocking leveldb my only real choice here? If so what's the recommended mocking framework for go? If there's another way what is it?

    if err == leveldb.ErrNotFound {
            store.Lock()
            perr := store.ldb.Put(itob(p.ID), p.ToBytes(), nil)
            if perr != nil {
                    store.Unlock()
                    return &StorerError{
                            Message: fmt.Sprintf("leveldb put error could not create puppy %d : %s", p.ID, perr),
                            Code:    501,
                    }
            }
            store.Unlock()
            return nil
    }

"Mocking out a db just to get test coverage up for a few edge cases seems like a lot of work" -- isn't that the entire reason mocks exist? Besides, you don't need to mock the entire db--just the parts your function depends on. — Jonathan Hall
– Jonathan Hall, Commented Jul 6, 2019 at 7:53

VonC · Accepted Answer · 2019-07-06 07:16:43Z

3

Mocking is the general chosen approach for this kind of test, which is why golang/mock, for instance, has a mockgen command, to generate the test code.

mockgen has two modes of operation: source and reflect.

Source mode generates mock interfaces from a source file.
It is enabled by using the -source flag.
Other flags that may be useful in this mode are -imports and -aux_files.

Example:
mockgen -source=foo.go [other options]
Reflect mode generates mock interfaces by building a program that uses reflection to understand interfaces.
It is enabled by passing two non-flag arguments: an import path, and a comma-separated list of symbols.

Example:
mockgen database/sql/driver Conn,Driver

answered Jul 6, 2019 at 7:16

VonC

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