assert: add Panics, PanicsWith

I want to use this for test coverage in microprom.

This turned out to be a bigger change than expected because testcapture
has a dependency on assert, which I had to invert to be able to use
testcapture.Capture() in assert.

1 files changed, 43 insertions, 0 deletions

diff --git a/testcapture/testcapture.go b/testcapture/testcapture.go
new file mode 100644
index 0000000..b0c0fac
--- /dev/null
+++ b/testcapture/testcapture.go
@@ -0,0 +1,43 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+// Package testcapture contains [Capture], a function that executes test code in a way that captures error messages and side effects without failing the overall test.
+//
+// The main intended use case is testing test assertions where calls to e.g. t.Error() are an expected part of a successful test run.
+package testcapture
+
+import (
+	"context"
+	"io"
+	"testing"
+)
+
+// TestingTB contains all the public functions of [testing.TB] (as of Go 1.26).
+// Functions in this package use this type instead of [testing.TB] because the capture device used by package testcapture cannot implement [testing.TB]: It contains methods that are private to the standard library.
+type TestingTB interface {
+	ArtifactDir() string
+	Attr(key, value string)
+	Chdir(dir string)
+	Cleanup(func())
+	Context() context.Context
+	Error(args ...any)
+	Errorf(format string, args ...any)
+	Fail()
+	Failed() bool
+	FailNow()
+	Fatal(args ...any)
+	Fatalf(format string, args ...any)
+	Helper()
+	Log(args ...any)
+	Logf(format string, args ...any)
+	Name() string
+	Output() io.Writer
+	Setenv(key, value string)
+	Skip(args ...any)
+	Skipf(format string, args ...any)
+	SkipNow()
+	Skipped() bool
+	TempDir() string
+}
+
+var _ TestingTB = testing.TB(nil)