test: add tests for target metadata tool handler

Signed-off-by: TJ Hoplock <[email protected]>

Author: tjhop

pkg/mcp/tools_test.go

@@ -606,3 +606,93 @@ func TestMetricMetadataToolHandler(t *testing.T) {
 		})
 	}
 }
+
+func TestTargetsMetadataToolHandler(t *testing.T) {
+	testCases := []struct {
+		name                    string
+		request                 mcp.CallToolRequest
+		mockTargetsMetadataFunc func(ctx context.Context, matchTarget string, metric string, limit string) ([]promv1.MetricMetadata, error)
+		validateResult          func(t *testing.T, result *mcp.CallToolResult, err error)
+	}{
+		{
+			name: "success with params",
+			request: mcp.CallToolRequest{
+				Request: mcp.Request{Method: string(mcp.MethodToolsCall)},
+				Params: mcp.CallToolParams{
+					Name: "targets_metadata",
+					Arguments: map[string]any{
+						"match_target": `{job="prometheus"}`,
+						"metric":       "go_goroutines",
+						"limit":        "10",
+					},
+				},
+			},
+			mockTargetsMetadataFunc: func(ctx context.Context, matchTarget string, metric string, limit string) ([]promv1.MetricMetadata, error) {
+				require.Equal(t, `{job="prometheus"}`, matchTarget)
+				require.Equal(t, "go_goroutines", metric)
+				require.Equal(t, "10", limit)
+				return []promv1.MetricMetadata{}, nil
+			},
+			validateResult: func(t *testing.T, result *mcp.CallToolResult, err error) {
+				require.NoError(t, err)
+				require.False(t, result.IsError)
+			},
+		},
+		{
+			name: "success no params",
+			request: mcp.CallToolRequest{
+				Request: mcp.Request{Method: string(mcp.MethodToolsCall)},
+				Params: mcp.CallToolParams{
+					Name: "targets_metadata",
+				},
+			},
+			mockTargetsMetadataFunc: func(ctx context.Context, matchTarget string, metric string, limit string) ([]promv1.MetricMetadata, error) {
+				return []promv1.MetricMetadata{}, nil
+			},
+			validateResult: func(t *testing.T, result *mcp.CallToolResult, err error) {
+				require.NoError(t, err)
+				require.False(t, result.IsError)
+			},
+		},
+		{
+			name: "API error",
+			request: mcp.CallToolRequest{
+				Request: mcp.Request{Method: string(mcp.MethodToolsCall)},
+				Params: mcp.CallToolParams{
+					Name: "targets_metadata",
+				},
+			},
+			mockTargetsMetadataFunc: func(ctx context.Context, matchTarget string, metric string, limit string) ([]promv1.MetricMetadata, error) {
+				return nil, errors.New("prometheus exploded")
+			},
+			validateResult: func(t *testing.T, result *mcp.CallToolResult, err error) {
+				require.NoError(t, err)
+				require.True(t, result.IsError)
+				require.Contains(t, toolCallResultAsString(result), "prometheus exploded")
+			},
+		},
+	}
+
+	mockAPI := &MockPrometheusAPI{}
+	mockServer := mcptest.NewUnstartedServer(t)
+	mockServer.AddTool(targetsMetadataTool, targetsMetadataToolHandler)
+
+	ctx := context.WithValue(context.Background(), apiClientKey{}, mockAPI)
+	err := mockServer.Start(ctx)
+	require.NoError(t, err)
+	defer mockServer.Close()
+
+	mcpClient := mockServer.Client()
+	defer mcpClient.Close()
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			mockAPI.TargetsMetadataFunc = tc.mockTargetsMetadataFunc
+
+			res, err := mcpClient.CallTool(ctx, tc.request)
+			require.NoError(t, err)
+
+			tc.validateResult(t, res, err)
+		})
+	}
+}