Add testsuite for high coverage, with measurements

Add cover.sh, a testsuite that builds goeval with coverage
instrumentation and executes goeval with various arguments to reach high
coverage.

So far we don't check goeval output.

The code of subcommands (packages ./sub/play, ./sub/share) isn't yet
measured: that will require to pass the -cover flags to 'go run' in
sub.go.

Author: dolmen

.gitignore

@@ -1 +1,7 @@
 /goeval
+
+# Output of cover.sh
+/.coverage
+/.coverage.out
+/goeval.cover
+/goeval-offline.cover

cover.sh

@@ -0,0 +1,114 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+output="${1:-.coverage.out}"
+GOCOVERDIR=.coverage
+go=go
+goeval=./goeval.cover
+goeval_offline=./goeval-offline.cover
+
+if ! command -v goimports >/dev/null; then
+        echo "goimports: command not found." >&2
+        exit 1
+fi
+
+if [[ ! -d "$GOCOVERDIR" ]]; then
+        mkdir -p "$GOCOVERDIR"
+else
+        rm -f "$GOCOVERDIR"/cov*
+fi
+
+unset GO111MODULE
+
+echo Building...
+
+$go build -covermode=set -coverpkg=./... -buildvcs=true -o=$goeval .
+$go build -covermode=set -coverpkg=./... -buildvcs=true -tags=goeval.offline -o=$goeval_offline .
+
+export GOCOVERDIR
+
+echo Running tests...
+
+# --------------------------------------------------------------
+
+$goeval || :
+$goeval -h || :
+
+$goeval 'fmt.Println("Hello, world")'
+
+# stdin
+$goeval - <<EOF
+fmt.Println("Hello, world")
+EOF
+
+$goeval -E 'fmt.Println("Hello, world")'
+
+$goeval -x 'fmt.Println("Hello, world")'
+
+
+# -i with comma
+# -i with . as alias
+# -i with _ as alias
+$goeval -i=.=fmt,time,_=os 'Println(time.Now())'
+
+# -o
+{
+        tmp_exe=$(mktemp -t goeval-cover)
+        $goeval -i=.=fmt,time -o "$tmp_exe" 'Println(time.Now())'
+        "$tmp_exe"
+        rm "$tmp_exe"
+}
+
+# With goimports builtin
+$goeval -goimports=goimports -E 'fmt.Println("Hello, world")'
+
+# Without goimports builtin
+$goeval -goimports= -E 'fmt.Println("Hello, world")'
+
+# With goimports as external command
+$goeval -goimports="$(command -v goimports)" -E 'fmt.Println("Hello, world")'
+
+
+# GOPATH mode with external package
+#GO111MODULE=off $go get github.com/klauspost/cpuid
+if [[ ! -d "$(go env GOPATH)"/src/github.com/klauspost/cpuid/v2 ]]; then
+        mkdir -p "$(go env GOPATH)"/src/github.com/klauspost/cpuid
+        cd "$(go env GOPATH)"/src/github.com/klauspost/cpuid
+        git clone "$(go env GOPATH)"/src/github.com/klauspost/cpuid.git v2
+fi
+GO111MODULE=off $goeval -i github.com/klauspost/cpuid/v2 'fmt.Println(cpuid.CPU.X64Level())'
+
+# Go module mode with external package
+$goeval -i cpuid=github.com/klauspost/cpuid/v2@v2.3.0 'fmt.Println(cpuid.CPU.X64Level())'
+
+# -E with Go module mode with external package
+$goeval -E -i cpuid=github.com/klauspost/cpuid/v2@v2.3.0 'fmt.Println(cpuid.CPU.X64Level())'
+
+$goeval -Eplay 'fmt.Println("Hello, world")'
+
+# -Eplay with Go module mode with external package
+$goeval -Eplay -i cpuid=github.com/klauspost/cpuid/v2@v2.3.0 'fmt.Println(cpuid.CPU.X64Level())'
+
+
+$goeval -play 'fmt.Println("Hello, world")'
+
+# -play with os.Args
+$goeval -play 'fmt.Println(os.Args[1])' 'Hello, world'
+
+$goeval_offline -h || :
+
+$goeval_offline 'fmt.Println("Hello, world")'
+
+$goeval_offline -play 'fmt.Println("Hello, world")' || :
+
+# We don't test -share here to not pollute play.golang.org
+# TODO(dolmen) Mock play.golang.org/share
+
+# -------------------------------------------------------------
+
+go tool covdata textfmt -i="$GOCOVERDIR" -o="$output"
+
+if [[ -t 0 ]] && command -v open >/dev/null; then
+        $go tool cover -html=$output
+fi