runtime: add tests for addrRanges.findSucc

This change adds a test suite for addrRanges.findSucc so we can change
the implementation more safely.

For #40191.

Change-Id: I14a834b6d54836cbc676eb0edb292ba6176705cc
Reviewed-on: https://go-review.googlesource.com/c/go/+/242678
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/runtime/export_test.go

@@ -785,6 +785,30 @@ func (a AddrRange) Equals(b AddrRange) bool {
 	return a == b
 }
 
+// AddrRanges is a wrapper around addrRanges for testing.
+type AddrRanges struct {
+	addrRanges
+}
+
+// MakeAddrRanges creates a new addrRanges populated with
+// the ranges in a.
+func MakeAddrRanges(a ...AddrRange) AddrRanges {
+	// Methods that manipulate the backing store of addrRanges.ranges should
+	// not be used on the result from this function (e.g. add) since they may
+	// trigger reallocation.
+	ranges := make([]addrRange, 0, len(a))
+	for _, r := range a {
+		ranges = append(ranges, r.addrRange)
+	}
+	return AddrRanges{addrRanges{ranges: ranges, sysStat: new(uint64)}}
+}
+
+// FindSucc returns the successor to base. See addrRanges.findSucc
+// for more details.
+func (a *AddrRanges) FindSucc(base uintptr) int {
+	return a.findSucc(base)
+}
+
 // BitRange represents a range over a bitmap.
 type BitRange struct {
 	I, N uint // bit index and length in bits