Include cross-package invocations in test coverage

The default behavior of `go test -cover` ignores coverage by integration
tests. That is, it ignores coverage by tests in a different package. This
penalizes Elvish since Elvish has a lot of integration tests that are
meant to indirectly, but explicitly, exercise code in other packages that
do not have explicit unit tests.

This change makes the test coverage more accurate for the purposes of
this project.

Resolves #1062
Resolves #1187

.appveyor.yml

@@ -4,11 +4,13 @@ environment:
   GOPATH: c:\gopath
   ELVISH_TEST_TIME_SCALE: 10
 install:
-  # Needed since the codecov uploader depends on a UNIX "find" command.
+  # The codecov uploader depends on a POSIX shell and commands such as `find`
+  # so ensure the relevant Windows MSYS2 directory is in the external command
+  # search path.
   - set PATH=C:\msys64\usr\bin;%PATH%
 build: off
 before_test:
   - go version
 test_script:
-  - go test -coverprofile=coverage -covermode=set ./...
-  - curl -s https://codecov.io/bash -o codecov && bash codecov -f coverage || ver > nul
+  - go test -coverprofile=cover -coverpkg=./pkg/... ./pkg/...
+  - curl -s https://codecov.io/bash -o codecov && bash codecov -f cover || ver > nul

.cirrus.yml

@@ -51,8 +51,8 @@ test_task:
   test_script: go test $TEST_FLAG ./...
   upload_coverage_script:
     - test -z $SKIP_UPLOAD_COVERAGE || exit 0
-    - go test -coverprofile=coverage -covermode=set ./...
-    - curl -s https://codecov.io/bash -o codecov && bash codecov -f coverage -t $CODECOV_TOKEN || true
+    - go test -coverprofile=cover -coverpkg=./pkg/... ./pkg/...
+    - curl -s https://codecov.io/bash -o codecov && bash codecov -f cover -t $CODECOV_TOKEN || true
 
 checkstyle_go_task:
   name: Check the style of .go files

Makefile

@@ -25,8 +25,9 @@ test:
 # Generate a basic test coverage report. This will open the report in your
 # browser. See also https://codecov.io/gh/elves/elvish/.
 cover:
-	go test -covermode=set -coverprofile=$@ ./...
-	go tool cover -html=$@
+	go test -coverprofile=cover -coverpkg=./pkg/... ./pkg/...
+	go tool cover -html=cover
+	go tool cover -func=cover | tail -1 | awk '{ print "Overall coverage:", $$NF }'
 
 # Ensure the style of Go and Markdown source files is consistent.
 style: