Run tests with code coverage (swiftlang#894)

To help identify poorly tested areas of the extension, run the tests
with code coverage. Coverage is reported in the terminal as text as well
as stored in the `/coverage` directory as HTML.

In CI results can be seen in the terminal at the end of the test run.
Locally when running tests in the docker containers HTML coverage
results will appear in the `/coverage` folder after the run completes.

Author: plemarquand

.c8rc

@@ -0,0 +1,14 @@
+{
+  "all": true,
+  "include": [
+    "out/**"
+  ],
+  "exclude": [
+    "**/node_modules/**",
+    "out/test/"
+  ],
+  "reporter": [
+    "text",
+    "html"
+  ]
+}

.gitignore

@@ -1,5 +1,6 @@
 out
 dist
+coverage
 node_modules
 default.profraw
 *.vsix

docker/docker-compose.yaml

@@ -34,7 +34,7 @@ services:
 
   test:
     <<: *common
-    command: /bin/bash -xcl "mkdir /tmp/code && cp -r ./ /tmp/code/ && cd /tmp/code && npm ci && npm run lint && npm run format && npm run package && ./docker/test.sh"
+    command: /bin/bash -xcl "./docker/test.sh"
 
   shell:
     <<: *common

docker/test.sh

@@ -1,2 +1,15 @@
-(xvfb-run -a npm test; echo $? > exitcode) | grep -Ev "Failed to connect to the bus|GPU stall due to ReadPixels"
+set -ex
+
+current_directory=$(pwd)
+
+mkdir /tmp/code
+cp -r ./ /tmp/code/
+cd /tmp/code
+
+npm ci
+npm run lint
+npm run format
+npm run package
+
+(xvfb-run -a npm run coverage; echo $? > exitcode) | grep -Ev "Failed to connect to the bus|GPU stall due to ReadPixels" && rm -rf "${current_directory}/coverage" && (cp -R ./coverage $current_directory || true)
 exit $(<exitcode)