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, 32 insertions, 0 deletions

diff --git a/assert/panic.go b/assert/panic.go
new file mode 100644
index 0000000..69828a4
--- /dev/null
+++ b/assert/panic.go
@@ -0,0 +1,32 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package assert
+
+import (
+	"go.xyrillian.de/gg/testcapture"
+)
+
+// Panics runs the provided action and fails the test if it does not panic.
+// On success, the error value passed to the call of panic is returned.
+func Panics(t TestingTB, action func()) any {
+	return PanicsWith[any](t, action)
+}
+
+// PanicsWith is like Panics(), but also checks if the recovered error value
+// is of type T, failing the test if the type assertion fails.
+func PanicsWith[T any](t TestingTB, action func()) T {
+	t.Helper()
+	result := testcapture.Capture(t.Context(), t.Name(), func(_ TestingTB) {
+		action()
+	})
+	if result.Outcome != testcapture.OutcomePanicked {
+		t.Fatal("did not panic")
+	}
+	value, ok := result.Panic.(T)
+	if !ok {
+		var zero T
+		t.Fatalf("panicked with incorrect type: expected %T, but got %#v", zero, result.Panic)
+	}
+	return value
+}