Consider updating declared Go version in go.mod

[JackMordaunt]

The go.mod file declares go 1.13 right now. Module graph pruning was added in Go 1.17, meaning that other modules can import your module and only pick up the transitive dependencies that are actually reachable based on how they use your code. Right now, importing testify means importing a yaml parser because the declared go version predates go 1.17.

The tidiest dependency graph will come from using go 1.18, as:

The go.sum file recorded by go mod tidy for a module by default includes checksums needed by the Go version one below the version specified in its go directive. So a go 1.17 module includes checksums needed for the full module graph loaded by Go 1.16, but a go 1.18 module will include only the checksums needed for the pruned module graph loaded by Go 1.17. The -compat flag can be used to override the default version (for example, to prune the go.sum file more aggressively in a go 1.17 module).

Go 1.18 is also the oldest Go release still supported by the Go team, so it's a reasonable choice of language version to declare.

[brackendawson]

Because of

unless that version of the module is also (transitively) required by some other dependency at go 1.16 or below

and because https://github.com/stretchr/objx requires testify at 1.13, objx would need to be updated first.

[dolmen]

Testify is a pillar in the Go ecosystem. As a maintainer I don't want to block users from upgrading Testify while they are locked on an older version of Go (for example for the support of a legacy GOOS or GOARCH).

So we will only upgrade the Go version only if necessary.

The minimum Go version currently declared in go.mod is 1.17. I don't see a need for an increase for now.