Implement plugin catalog and discovery system

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

internal/plugin/completion_test.go

@@ -0,0 +1,80 @@
+/*
+Copyright 2026 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package plugin
+
+import (
+	"testing"
+
+	"github.com/spf13/cobra"
+)
+
+func TestParseCompletionOutput(t *testing.T) {
+	tests := []struct {
+		name                string
+		input               string
+		expectedCompletions []string
+		expectedDirective   cobra.ShellCompDirective
+	}{
+		{
+			name:                "standard output",
+			input:               "instance\nrset\nrsip\nall\n:4\n",
+			expectedCompletions: []string{"instance", "rset", "rsip", "all"},
+			expectedDirective:   cobra.ShellCompDirective(4),
+		},
+		{
+			name:                "default directive",
+			input:               "foo\nbar\n:0\n",
+			expectedCompletions: []string{"foo", "bar"},
+			expectedDirective:   cobra.ShellCompDirectiveDefault,
+		},
+		{
+			name:                "with descriptions",
+			input:               "get\tGet resources\nbuild\tBuild resources\n:4\n",
+			expectedCompletions: []string{"get\tGet resources", "build\tBuild resources"},
+			expectedDirective:   cobra.ShellCompDirective(4),
+		},
+		{
+			name:                "empty completions",
+			input:               ":4\n",
+			expectedCompletions: nil,
+			expectedDirective:   cobra.ShellCompDirective(4),
+		},
+		{
+			name:                "empty input",
+			input:               "",
+			expectedCompletions: nil,
+			expectedDirective:   cobra.ShellCompDirectiveError,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			completions, directive := parseCompletionOutput(tt.input)
+			if directive != tt.expectedDirective {
+				t.Errorf("directive: got %d, want %d", directive, tt.expectedDirective)
+			}
+			if len(completions) != len(tt.expectedCompletions) {
+				t.Fatalf("completions count: got %d, want %d", len(completions), len(tt.expectedCompletions))
+			}
+			for i, c := range completions {
+				if c != tt.expectedCompletions[i] {
+					t.Errorf("completion[%d]: got %q, want %q", i, c, tt.expectedCompletions[i])
+				}
+			}
+		})
+	}
+}