assert.Contains with []byte should match string

[kristiyanpd]

Description

When using assert.Contains on byte slices, the assertion fails even if the expected subsequence exists.

Environment:

• Go version: 1.23
• Testify version: v1.10.0

Step To Reproduce

func Test(t *testing.T) {
	slice1 := []byte(`Hello World Hello`)
	slice2 := []byte(`World`)

	// This assertion fails, even though slice1 does contain slice2.
	assert.Contains(t, slice1, slice2)

	// These alternatives work as expected:
	assert.Contains(t, string(slice1), string(slice2))

	if !bytes.Contains(slice1, slice2) {
		t.Errorf("Expected slice1 to contain %q", slice2)
	}
}

Expected behavior

The assert.Contains function should pass when a byte slice contains another byte slice. This behavior is consistent with the expectation that the function would detect the presence of a subsequence within a byte array.

Actual behavior

The test fails when using assert.Contains on byte slices, which indicates that the assertion function does not properly support byte slice containment checks.

[debug-ing]

Hello, I will solve this issue.

[Antonboom]

Related to https://github.com/stretchr/testify/pull/1526

[brackendawson]

As mentioned in #1526, we have chosen not to give []byte behavior equivalent to that of string in assert.Contains because:

• Contains has already been inappropriately overloaded with slice/array contains element behavior: Contains(t, []byte{1}, 1)
• The string behavior works for all string kinds including named types, this is difficult to map onto []byte, should it work with these types?

  type mySlice []byte
  // mySlice("how about it?")
  type myByte byte
  // []myByte{}
  type myOtherSlice []myByte
  // myOtherSlice{}
  

Because of these properties and their interactions; the resulting Contains assertion is too complicated to properly document, maintain and use.

Anyone looking for the functionality should use a conversion:

slice1 := []byte(`Hello World Hello`)
slice2 := []byte(`World`)
assert.Contains(t, string(slice1), string(slice2))