From cd82460513d5abf04e56c01667d56499d4c354be Mon Sep 17 00:00:00 2001
From: kegsay <kegan@matrix.org>
Date: Tue, 17 May 2022 10:45:50 +0100
Subject: Add docs which explain how to calculate coverage (#2468)

---
 docs/coverage.md | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 docs/coverage.md

diff --git a/docs/coverage.md b/docs/coverage.md
new file mode 100644
index 00000000..7a3b7cb9
--- /dev/null
+++ b/docs/coverage.md
@@ -0,0 +1,84 @@
+---
+title: Coverage
+parent: Development
+permalink: /development/coverage
+---
+
+To generate a test coverage report for Sytest, a small patch needs to be applied to the Sytest repository to compile and use the instrumented binary:
+```patch
+diff --git a/lib/SyTest/Homeserver/Dendrite.pm b/lib/SyTest/Homeserver/Dendrite.pm
+index 8f0e209c..ad057e52 100644
+--- a/lib/SyTest/Homeserver/Dendrite.pm
++++ b/lib/SyTest/Homeserver/Dendrite.pm
+@@ -337,7 +337,7 @@ sub _start_monolith
+ 
+    $output->diag( "Starting monolith server" );
+    my @command = (
+-      $self->{bindir} . '/dendrite-monolith-server',
++      $self->{bindir} . '/dendrite-monolith-server', '--test.coverprofile=' . $self->{hs_dir} . '/integrationcover.log', "DEVEL",
+       '--config', $self->{paths}{config},
+       '--http-bind-address', $self->{bind_host} . ':' . $self->unsecure_port,
+       '--https-bind-address', $self->{bind_host} . ':' . $self->secure_port,
+diff --git a/scripts/dendrite_sytest.sh b/scripts/dendrite_sytest.sh
+index f009332b..7ea79869 100755
+--- a/scripts/dendrite_sytest.sh
++++ b/scripts/dendrite_sytest.sh
+@@ -34,7 +34,8 @@ export GOBIN=/tmp/bin
+ echo >&2 "--- Building dendrite from source"
+ cd /src
+ mkdir -p $GOBIN
+-go install -v ./cmd/dendrite-monolith-server
++# go install -v ./cmd/dendrite-monolith-server
++go test -c -cover -covermode=atomic -o $GOBIN/dendrite-monolith-server -coverpkg "github.com/matrix-org/..." ./cmd/dendrite-monolith-server
+ go install -v ./cmd/generate-keys
+ cd -
+ ```
+
+ Then run Sytest. This will generate a new file `integrationcover.log` in each server's directory e.g `server-0/integrationcover.log`. To parse it,
+ ensure your working directory is under the Dendrite repository then run:
+ ```bash
+ go tool cover -func=/path/to/server-0/integrationcover.log
+ ```
+ which will produce an output like:
+ ```
+ ...
+ github.com/matrix-org/util/json.go:83:											NewJSONRequestHandler				100.0%
+github.com/matrix-org/util/json.go:90:											Protect						57.1%
+github.com/matrix-org/util/json.go:110:											RequestWithLogging				100.0%
+github.com/matrix-org/util/json.go:132:											MakeJSONAPI					70.0%
+github.com/matrix-org/util/json.go:151:											respond						61.5%
+github.com/matrix-org/util/json.go:180:											WithCORSOptions					0.0%
+github.com/matrix-org/util/json.go:191:											SetCORSHeaders					100.0%
+github.com/matrix-org/util/json.go:202:											RandomString					100.0%
+github.com/matrix-org/util/json.go:210:											init						100.0%
+github.com/matrix-org/util/unique.go:13:										Unique						91.7%
+github.com/matrix-org/util/unique.go:48:										SortAndUnique					100.0%
+github.com/matrix-org/util/unique.go:55:										UniqueStrings					100.0%
+total:															(statements)					53.7%
+```
+The total coverage for this run is the last line at the bottom. However, this value is misleading because Dendrite can run in many different configurations,
+which will never be tested in a single test run (e.g sqlite or postgres, monolith or polylith). To get a more accurate value, additional processing is required
+to remove packages which will never be tested and extension MSCs:
+```bash
+# These commands are all similar but change which package paths are _removed_ from the output.
+
+# For Postgres (monolith)
+go tool cover -func=/path/to/server-0/integrationcover.log | grep 'github.com/matrix-org/dendrite' | grep -Ev 'inthttp|sqlite|setup/mscs|api_trace' > coverage.txt
+
+# For Postgres (polylith)
+go tool cover -func=/path/to/server-0/integrationcover.log | grep 'github.com/matrix-org/dendrite' | grep -Ev 'sqlite|setup/mscs|api_trace' > coverage.txt
+
+# For SQLite (monolith)
+go tool cover -func=/path/to/server-0/integrationcover.log | grep 'github.com/matrix-org/dendrite' | grep -Ev 'inthttp|postgres|setup/mscs|api_trace' > coverage.txt
+
+# For SQLite (polylith)
+go tool cover -func=/path/to/server-0/integrationcover.log | grep 'github.com/matrix-org/dendrite' | grep -Ev 'postgres|setup/mscs|api_trace' > coverage.txt
+```
+
+A total value can then be calculated using:
+```bash
+cat coverage.txt | awk -F '\t+' '{x = x + $3} END {print x/NR}'
+```
+
+
+We currently do not have a way to combine Sytest/Complement/Unit Tests into a single coverage report.
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