fix(install): duplicate dependencies in `package.json` (#26128)

Fixes https://github.com/denoland/deno/issues/26120

1 files changed, 16 insertions, 0 deletions

diff --git a/tests/specs/install/install_add_dev_existing/__test__.jsonc b/tests/specs/install/install_add_dev_existing/__test__.jsonc
new file mode 100644
index 000000000..e4e2f8a31
--- /dev/null
+++ b/tests/specs/install/install_add_dev_existing/__test__.jsonc
@@ -0,0 +1,16 @@
+{
+  "tempDir": true,
+  "steps": [
+    {
+      "args": "install --dev npm:@denotest/esm-basic",
+      "output": "install.out"
+    },
+    {
+      "args": [
+        "eval",
+        "console.log(Deno.readTextFileSync('package.json').trim())"
+      ],
+      "output": "package.json.out"
+    }
+  ]
+}