test(e2e): tier-1 dry-run smoke, no cluster/creds (#14)

Drives the assembled pipeline through the CLI over testdata/gitops-repo (a raw
Deployment whose namespace is omitted + a KRR JSON proposing a downsize):
KRR -> adapter -> discover -> policy -> yamledit, printed as a real unified
diff. Asserts exit 0, the diff shows the downsized cpu/mem and the removed CPU
limit, and the on-disk fixture is byte-for-byte unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Ca-moes

e2e/e2e_test.go

@@ -0,0 +1,62 @@
+// Package e2e exercises the assembled rere pipeline end-to-end through the CLI,
+// using no mocks: KRR JSON -> adapter -> discover -> policy -> yamledit, with
+// the result printed as a dry-run diff. No cluster and no credentials.
+package e2e
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/Ca-moes/rere/internal/cli"
+)
+
+func TestDryRunDownsize(t *testing.T) {
+	repo := filepath.Join("testdata", "gitops-repo")
+	manifest := filepath.Join(repo, "deployment.yaml")
+
+	before, err := os.ReadFile(manifest)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	root := cli.NewRootCommand("test", "none", "now")
+	var out bytes.Buffer
+	root.SetOut(&out)
+	root.SetErr(&out)
+	root.SetArgs([]string{
+		"run", "--dry-run",
+		"--repo", repo,
+		"--input", filepath.Join(repo, "krr.json"),
+	})
+
+	if err := root.Execute(); err != nil {
+		t.Fatalf("rere run --dry-run failed: %v\noutput:\n%s", err, out.String())
+	}
+
+	got := out.String()
+	// The diff is real (produced by yamledit) and shows the downsize.
+	if !strings.Contains(got, "@@") {
+		t.Errorf("expected a unified diff, got:\n%s", got)
+	}
+	if !strings.Contains(got, "250m") {
+		t.Errorf("diff missing downsized cpu (250m):\n%s", got)
+	}
+	if !strings.Contains(got, "deployment.yaml") {
+		t.Errorf("diff missing file header:\n%s", got)
+	}
+	// The CPU limit should be removed (a deletion line carrying the old "2").
+	if !strings.Contains(got, `-              cpu: "2"`) {
+		t.Errorf("expected cpu limit removal in diff:\n%s", got)
+	}
+
+	after, err := os.ReadFile(manifest)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(before, after) {
+		t.Error("dry-run modified the on-disk fixture")
+	}
+}

e2e/testdata/gitops-repo/deployment.yaml

@@ -0,0 +1,19 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: web
+  # namespace intentionally omitted (kustomize sets it); rere still matches.
+spec:
+  replicas: 2
+  template:
+    spec:
+      containers:
+        - name: app
+          image: web:1.0 # pinned
+          resources:
+            requests:
+              cpu: "1"
+              memory: 1Gi
+            limits:
+              cpu: "2"
+              memory: 1Gi

e2e/testdata/gitops-repo/krr.json

@@ -0,0 +1,27 @@
+{
+  "scans": [
+    {
+      "object": {
+        "namespace": "default",
+        "kind": "Deployment",
+        "name": "web",
+        "container": "app",
+        "allocations": {
+          "requests": {"cpu": 1.0, "memory": 1073741824},
+          "limits": {"cpu": 2.0, "memory": 1073741824}
+        }
+      },
+      "recommended": {
+        "requests": {
+          "cpu": {"value": 0.25, "severity": "WARNING"},
+          "memory": {"value": 268435456, "severity": "WARNING"}
+        },
+        "limits": {
+          "cpu": {"value": null, "severity": "OK"},
+          "memory": {"value": 268435456, "severity": "OK"}
+        }
+      },
+      "severity": "WARNING"
+    }
+  ]
+}