assert: more unsafe.Pointer tests

1. Isolate tests that use the "unsafe" package in a separate package
   assert/internal/unsafetests. That way the assert package is not
   tainted with unsafe.
2. Remove one reference to the private assert.isNil() in assert tests.
3. Add more tests of assert.Nil and assert.NotNil with unsafe.Pointer.

assert/assertions_test.go

@@ -16,7 +16,6 @@ import (
 	"strings"
 	"testing"
 	"time"
-	"unsafe"
 )
 
 var (
@@ -3138,10 +3137,3 @@ func TestErrorAs(t *testing.T) {
 		})
 	}
 }
-
-func TestIsNil(t *testing.T) {
-	var n unsafe.Pointer = nil
-	if !isNil(n) {
-		t.Fatal("fail")
-	}
-}

assert/internal/unsafetests/doc.go

@@ -0,0 +1,4 @@
+// This package exists just to isolate tests that reference the [unsafe] package.
+//
+// The tests in this package are totally safe.
+package unsafetests

assert/internal/unsafetests/unsafetests_test.go

@@ -0,0 +1,34 @@
+package unsafetests_test
+
+import (
+	"fmt"
+	"testing"
+	"unsafe"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type ignoreTestingT struct{}
+
+var _ assert.TestingT = ignoreTestingT{}
+
+func (ignoreTestingT) Helper() {}
+
+func (ignoreTestingT) Errorf(format string, args ...interface{}) {
+	// Run the formatting, but ignore the result
+	msg := fmt.Sprintf(format, args...)
+	_ = msg
+}
+
+func TestUnsafePointers(t *testing.T) {
+	var ignore ignoreTestingT
+
+	assert.True(t, assert.Nil(t, unsafe.Pointer(nil), "unsafe.Pointer(nil) is nil"))
+	assert.False(t, assert.NotNil(ignore, unsafe.Pointer(nil), "unsafe.Pointer(nil) is nil"))
+
+	assert.True(t, assert.Nil(t, unsafe.Pointer((*int)(nil)), "unsafe.Pointer((*int)(nil)) is nil"))
+	assert.False(t, assert.NotNil(ignore, unsafe.Pointer((*int)(nil)), "unsafe.Pointer((*int)(nil)) is nil"))
+
+	assert.False(t, assert.Nil(ignore, unsafe.Pointer(new(int)), "unsafe.Pointer(new(int)) is NOT nil"))
+	assert.True(t, assert.NotNil(t, unsafe.Pointer(new(int)), "unsafe.Pointer(new(int)) is NOT nil"))
+}