This PR is to add comments to TestParseReportMetric in pkg/ddc/alluxio/report_test.go (#5030)

* Add English comments to TestParseReportMetric in report_test.go

Signed-off-by: akie <221850025@smail.nju.edu.cn>

* Add comments to TestParseReportMetric in pkg/ddc/alluxio/report_test.go

Signed-off-by: akie <221850025@smail.nju.edu.cn>

---------

Signed-off-by: akie <221850025@smail.nju.edu.cn>
Co-authored-by: akie <221850025@smail.nju.edu.cn>

Author: akiefufu

pkg/ddc/alluxio/report_test.go

@@ -43,6 +43,22 @@ func TestParseReportSummary(t *testing.T) {
 	}
 }
 
+// TestParseReportMetric tests the ParseReportMetric method of the AlluxioEngine struct.
+// It defines multiple test cases to verify the correctness of metric parsing and calculation of cache hit states.
+//
+// Each test case provides:
+// - 'metrics': input string representing raw metrics data.
+// - 'lastCacheHitStates': the previous cache hit state, which may be nil for initial parsing.
+// - 'want': the expected cacheHitStates result after parsing.
+//
+// The test checks two scenarios:
+//  1. When there is no previous cache hit state (lastCacheHitStates is nil),
+//     it verifies that the parsed bytesReadLocal and bytesReadUfsAll values are correct.
+//  2. When a previous cache hit state exists, it also checks the computed cache hit ratios
+//     and throughput ratios for correctness using deep equality.
+//
+// If the actual output differs from the expected output, the test reports an error
+// with detailed information for debugging.
 func TestParseReportMetric(t *testing.T) {
 	testCases := map[string]struct {
 		metrics            string