Keep a fill warning for an unreadable bucket or log only when its condition was read open

Second review of #231: when neither the stream nor its condition can be
read, nothing is known of its fill, so none is said; the unread warning
covers it. Only a condition read back as open is kept, with its own words.

cmd/mesh-controller/bucket_log_fill_test.go

@@ -84,12 +84,12 @@ func TestAnUnreadableBucketOrLogIsSaidAndTheRestAreStillJudged(t *testing.T) {
 		}
 		return filled{}, false, nil
 	}
-	open := func(_ context.Context, key string) (conditions.Condition, bool) {
+	open := func(_ context.Context, key string) (conditions.Condition, bool, error) {
 		if key == fillKey(brokenOpen) {
 			return conditions.Condition{Key: key, Severity: conditions.Warning,
-				Summary: "a's log was-filling holds 800.0 MiB of 1024.0 MiB, 78%"}, true
+				Summary: "a's log was-filling holds 800.0 MiB of 1024.0 MiB, 78%"}, true, nil
 		}
-		return conditions.Condition{}, false
+		return conditions.Condition{}, false, nil
 	}
 	got := map[string]conditions.Observation{}
 	for _, o := range judgeFills(context.Background(), []bucketOrLog{broken, brokenOpen, full, empty, absent}, read, open) {
@@ -128,3 +128,38 @@ func TestAFillingOrUnreadBucketOrLogIsSaidInPlainWords(t *testing.T) {
 		}
 	}
 }
+
+// **When neither the bucket or log nor its condition can be read, nothing is said of its fill** (second
+// review of #231): the unread finding covers it, and no fill is invented for it. For one that is read and
+// measured between seven tenths and three quarters, a condition that cannot be read is taken as open, so
+// an unknown never clears it.
+func TestNothingIsSaidOfAFillWhenNeitherItNorItsConditionCanBeRead(t *testing.T) {
+	const mib = 1024 * 1024
+	broken := bucketOrLog{Module: "a", Kind: "log", Name: "changes", Stream: "LOG_a_changes"}
+	between := bucketOrLog{Module: "b", Kind: "bucket", Name: "issues", Stream: "KV_b_issues"}
+	read := func(_ context.Context, s bucketOrLog) (filled, bool, error) {
+		if s == broken {
+			return filled{}, false, errors.New("the bus did not answer")
+		}
+		return filled{Bytes: 72 * mib, Max: 100 * mib}, true, nil
+	}
+	open := func(context.Context, string) (conditions.Condition, bool, error) {
+		return conditions.Condition{}, false, errors.New("the conditions bucket did not answer")
+	}
+	got := map[string]conditions.Observation{}
+	for _, o := range judgeFills(context.Background(), []bucketOrLog{broken, between}, read, open) {
+		got[o.Key()] = o
+	}
+	if o, said := got[fillKey(broken)]; said {
+		t.Fatalf("a fill was said for a log whose fill and condition could not be read: %+v", o)
+	}
+	if _, said := got[conditions.Key(conditions.ScopeBus, broken.Stream, "unread")]; !said {
+		t.Error("the log that could not be read was not said as unread")
+	}
+	if _, kept := got[fillKey(between)]; !kept {
+		t.Error("a bucket at 72% whose condition could not be read was cleared")
+	}
+	if len(got) != 2 {
+		t.Errorf("said %d findings, want 2: %v", len(got), got)
+	}
+}