test(observability-proxy): pin the concurrency Retry-After value

The test only checked that a Retry-After was present, while the rate
limit test pins its value, so a change to the promised hint passed.
It now expects the literal value. The note on the empty fields_limit
case now gives the reason it is refused.

Assisted-by: LLM
Signed-off-by: ZverGuy <maximbel2003@gmail.com>

internal/observabilityproxy/logsparams_test.go

@@ -116,7 +116,7 @@ func TestBuildLogsParamsRejects(t *testing.T) {
 		code     int
 	}{
 		{"unknown endpoint", "tenant_ids", url.Values{}, http.StatusNotFound},
-		// vlselect reads fields_limit=0 as no limit on the groups.
+		// Malformed rather than a request for the default.
 		{"empty fields_limit", "hits", url.Values{"field": {"level"}, "fields_limit": {""}}, http.StatusBadRequest},
 		{"stats_query is not proxied", "stats_query", url.Values{}, http.StatusNotFound},
 		{"ignore_global_time_filter", "query", url.Values{"query": {`* options(ignore_global_time_filter=true)`}}, http.StatusBadRequest},

internal/observabilityproxy/server_test.go

@@ -488,8 +488,8 @@ func TestServerConcurrencyRetryAfter(t *testing.T) {
 		defer func() { _ = first.Body.Close() }()
 		second := h.do(http.MethodGet, logsRoot+endpoint, "good", nil, nil)
 		_ = second.Body.Close()
-		if second.StatusCode != http.StatusTooManyRequests || second.Header.Get("Retry-After") == "" {
-			t.Errorf("%s over the limit answered %d with Retry-After %q, want 429 with a value",
+		if second.StatusCode != http.StatusTooManyRequests || second.Header.Get("Retry-After") != "1" {
+			t.Errorf("%s over the limit answered %d with Retry-After %q, want 429 with 1",
 				endpoint, second.StatusCode, second.Header.Get("Retry-After"))
 		}
 	}