From 1891db3814cdc73404f5148f96871f8bfef76331 Mon Sep 17 00:00:00 2001
From: Jim Pivarski <jpivarski@gmail.com>
Date: Tue, 8 Aug 2023 16:56:31 -0500
Subject: [PATCH] ListOffsetArray's is_valid.

---
 src/AwkwardArray.jl | 7 ++++++-
 test/runtests.jl    | 9 +++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/AwkwardArray.jl b/src/AwkwardArray.jl
index fb6ed62..ebb9d86 100644
--- a/src/AwkwardArray.jl
+++ b/src/AwkwardArray.jl
@@ -63,7 +63,12 @@ struct ListOffsetArray{T<:Union{Int32,UInt32,Int64}} <: Content
 end
 
 function is_valid(x::ListOffsetArray)
-    true
+    for i = Base.firstindex(x):Base.lastindex(x)
+        if x.offsets[i+1] < x.offsets[i]
+            return false
+        end
+    end
+    return true
 end
 
 function Base.length(x::ListOffsetArray)
diff --git a/test/runtests.jl b/test/runtests.jl
index 033dead..2b4d13b 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -39,4 +39,13 @@ using Test
         end
         @test tmp == 5
     end
+
+    begin
+        layout = AwkwardArray.ListOffsetArray(
+            [0, 3, 2, 5],
+            AwkwardArray.PrimitiveArray([1.1, 2.2, 3.3, 4.4, 5.5]),
+        )
+        @test !AwkwardArray.is_valid(layout)
+    end
+
 end