feat: Add append_dimensions tests for collectd, ethtool, and cpu plugins

[TravisStark]

Description of the issue

The CloudWatch Agent supports append_dimensions at two configuration levels with different behaviors:

• Global level (metrics.append_dimensions): Adds EC2 metadata dimensions and drops the host dimension
• Plugin level (metrics_collected.<plugin>.append_dimensions): Adds dimensions while keeping the host dimension

There were no integration tests validating this behavioral difference for collectd, CPU, or ethtool plugins. This gap made it difficult to catch regressions in dimension handling logic.

Description of changes

Added comprehensive integration tests for append_dimensions support across multiple plugins:

Collectd tests:

• CollectdNoAppendDimensions - Baseline: verifies host is present and InstanceId is absent without configuration
• CollectdGlobalAppendDimensions - Verifies global config adds InstanceId/InstanceType and drops host
• CollectdAppendDimensions - Verifies plugin-level config adds dimensions while keeping host
• CollectdFleetAggregation - Verifies plugin-level config works with aggregation_dimensions

CPU tests:

• CpuGlobalAppendDimensions - Verifies global config behavior for CPU metrics

Ethtool tests:

• EthtoolAppendDimensions - Verifies global config drops host
• EthtoolPluginAppendDimensions - Verifies plugin-level config keeps host

Infrastructure improvements:

• Added ethtool_test_helpers.go
• Updated metrics_dimension_test.go with dynamic column widths in summary table
• Added test descriptions map for CI-friendly output

License

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Tests

• Test Run
• Passing Metric Dimensions Test
• All new test files compile successfully with go build ./...
• Tests follow existing patterns in the metric_dimension test suite
• Each test validates both positive cases (expected dimensions present) and negative cases (unexpected dimensions absent)
• Collectd tests use common.SendCollectDMetrics() to generate test data

[the-mann]

Can you extract the common validation logic? The 7 test files have significant duplication. A shared helper function for dimension validation would reduce this.

[the-mann]

code review agent:

Code Review: PR #647

PR: feat: Add append_dimensions tests for collectd, ethtool, and cpu plugins
Author: TravisStark
Branch: tjstark/collectd-append → main
Changes: 19 files, +1138/-109 lines

CI Status

⚠️ No workflow runs found for current commit SHA (9dbae34)

---

Findings

Major

1. CollectdFleetAggregationTestRunner doesn't use shared helpers

File: collectd_fleet_aggregation_test.go:68-179

This test manually constructs dimensions instead of using the new DimensionSpec helpers that all other tests use. This defeats the refactoring purpose and creates inconsistency.

Suggested fix:

func (t *CollectdFleetAggregationTestRunner) validateCollectdFleetAggregationMetric(metricName string) status.TestResult {
    metricType := metric.GetCollectDMetricType(metricName)
    ns := "CollectdFleetAggregationTest"

    // Test 1: Fleet-aggregated dimensions
    fleetSpecs := []DimensionSpec{
        ExactDim("Component", "WebServer"),
        ExactDim("type", metricType),
    }
    result := ValidateDimensionsPresent(&t.BaseTestRunner, ns, metricName, fleetSpecs)
    if result.Status != status.SUCCESSFUL {
        return result
    }

    // Test 2: Per-instance dimensions
    instanceSpecs := []DimensionSpec{
        ExactDim("Component", "WebServer"),
        ExactDim("type", metricType),
        {Key: "InstanceId"},
    }
    result = ValidateDimensionsPresent(&t.BaseTestRunner, ns, metricName, instanceSpecs)
    if result.Status != status.SUCCESSFUL {
        return result
    }

    // Test 3: Host dimension kept
    hostSpecs := []DimensionSpec{
        ExactDim("Component", "WebServer"),
        ExactDim("type", metricType),
        HostDim(),
    }
    return ValidateDimensionsPresent(&t.BaseTestRunner, ns, metricName, hostSpecs)
}

---

Minor

2. Hardcoded driver name "ena"

File: ethtool_append_dimensions_test.go:68-69

ExactDim("driver", "ena"),

Consider adding a comment noting this is EC2-specific.

3. Changed log.Printf to fmt.Printf

File: metrics_dimension_test.go:190-200

This removes timestamps from output. Verify this is intentional.

4. printTestSummaryTable adds 70+ lines to test file

File: metrics_dimension_test.go:55-127

Consider moving to a separate helper file.

---

Positive Observations

• Good test coverage (positive and negative cases)
• Excellent documentation of global vs plugin-level append_dimensions behavior
• Refactoring reduces duplication via dimension_validation_helpers.go
• Follows existing ITestRunner patterns
• Correct //go:build !windows tags

---

Verdict

Approve with minor suggestions

Main concern: CollectdFleetAggregationTestRunner should use shared helpers for consistency.

[the-mann]

please rerun tests with refactor and i'll approve

[the-mann]

you can ignore the other stuff kiro mentioned btw i think it's all too minor to act on