For those who find this when googling (like I was), while master does include assertions for this, it is not present in the current release (1.3.0). The documentation reflects master, rather than the current release.

If you want to do this in the current release, you can do something like this

// Cannot call this more times than we have values for
assert.True(t, func() bool {
	return readCursor < len(pasteContents)
}())

You can use assert.Less

	assert.Less(t, 3, 4) // passes
	assert.Less(t, 4, 3) // fails

doc here

@kandros This is not present in the current release, only in master.