Be

Package be is the minimalist testing helper for Go.

Inspired by Mat Ryer and Alex Edwards.

Features

• Simple and readable test assertions using generics
• Built-in helpers for common cases like be.NilErr and be.In
• Fail fast by default but easily switch to relaxed with be.Relaxed(t)
• Helpers for testing against golden files with the testfile subpackage
• No dependencies: just uses standard library

Example usage

Test for simple equality using generics:

// Test two unequal strings
be.Equal(t, "hello", "world")     // bad
// t.Fatal("want: hello; got: world")
// Test two equal strings
be.Equal(t, "goodbye", "goodbye") // good
// Test equal integers, etc.
be.Equal(t, 200, resp.StatusCode)
be.Equal(t, tc.wantPtr, gotPtr)

// Test for inequality
be.Unequal(t, "hello", "world")     // good
be.Unequal(t, "goodbye", "goodbye") // bad
// t.Fatal("got: goodbye")

Test for equality of slices:

s := []int{1, 2, 3}
be.AllEqual(t, []int{1, 2, 3}, s) // good
be.AllEqual(t, []int{3, 2, 1}, s) // bad
// t.Fatal("want: [3 2 1]; got: [1 2 3]")

Handle errors:

var err error
be.NilErr(t, err)   // good
be.Nonzero(t, err) // bad
// t.Fatal("got: <nil>")
err = errors.New("(O_o)")
be.NilErr(t, err)   // bad
// t.Fatal("got: (O_o)")
be.Nonzero(t, err) // good

Check substring containment:

be.In(t, "world", "hello, world") // good
be.In(t, "World", "hello, world") // bad
// t.Fatal("World" not in "hello, world")
be.NotIn(t, "\x01", []byte("\a\b\x00\r\t")) // good
be.NotIn(t, "\x00", []byte("\a\b\x00\r\t")) // bad
// t.Fatal("\x00" in "\a\b\x00\r\t")

Test anything else:

be.True(t, o.IsValid())
be.True(t, len(pages) >= 20)

Test using goldenfiles:

// Start a sub-test for each .txt file
testfile.Run(t, "testdata/*.txt", func(t *testing.T, path string) {
	// Read the file
	input := testfile.Read(t, path)

	// Do some conversion on it
	type myStruct struct{ Whatever string }
	got := myStruct{strings.ToUpper(input)}

	// See if the struct is equivalent to a .json file
	wantFile := strings.TrimSuffix(path, ".txt") + ".json"
	testfile.EqualJSON(t, wantFile, got)

	// If it's not equivalent,
	// the got struct will be dumped
	// to a file named testdata/-failed-test-name.json
})

Philosophy

Tests usually should not fail. When they do fail, the failure should be repeatable. Therefore, it doesn't make sense to spend a lot of time writing good test messages. (This is unlike error messages, which should happen fairly often, and in production, irrepeatably.) Package be is designed to simply fail a test quickly and quietly if a condition is not met with a reference to the line number of the failing test. If the reason for having the test is not immediately clear from context, you can write a comment, just like in normal code. If you do need more extensive reporting to figure out why a test is failing, use be.DebugLog or be.Debug to capture more information.

Most tests just need simple equality testing, which is handled by be.Equal (for comparable types), be.AllEqual (for slices of comparable types), and be.DeepEqual (which relies on reflect.DeepEqual). Another common test is that a string or byte slice should contain or not some substring, which is handled by be.In and be.NotIn. Rather than package be providing every possible test helper, you are encouraged to write your own advanced helpers for use with be.True, while package be takes away the drudgery of writing yet another simple func nilErr(t *testing.T, err) { ... }.

The testfile subpackage has functions that make it easy to write file-based tests that ensure that the output of some transformation matches a golden file. Subtests can automatically be run for all files matching a glob pattern, such as testfile.Run(t, "testdata/*/input.txt", ...). If the test fails, the failure output will be written to a file, such as "testdata/basic-test/-failed-output.txt", and then the output can be examined via diff testing with standard tools. Set the environmental variable TESTFILE_UPDATE to update the golden file.

Every tool in the be module requires a testing.TB as its first argument. There are various clever ways to get the testing.TB implicitly, but package be is designed to be simple and explicit, so it's easiest to just always pass in a testing.TB the boring way.