Fail fast in tests if avalancheGo executable isn't an absolute path

Currently when running ginkgo tests with --avalanchego flag with a relative path,
the tests fail when trying to ascertain the rpcvm plugin path, because they execute the binary
without an absolute path, and the binary path is evaluated from a wrong location.

In order to make the underlying issue clear, I added a check that fails the test
and warns that an absolute path must be used.

Signed-off-by: Yacov Manevich <[email protected]>

Author: yacovm

tests/e2e/README.md

@@ -8,7 +8,7 @@
 ```bash
 ./scripts/build.sh        # Builds avalanchego for use in deploying a test network
 ./scripts/build_xsvm.sh   # Builds xsvm for use in deploying a test network with a subnet
-./bin/ginkgo -v ./tests/e2e -- --avalanchego-path=./build/avalanchego
+./bin/ginkgo -v ./tests/e2e -- --avalanchego-path=$PWD/build/avalanchego # Note that the path given for --avalanchego-path must be an absolute and not a relative path.
 ```
 
 See [`tests.e2e.sh`](../../scripts/tests.e2e.sh) for an example.

tests/fixture/e2e/flags.go

@@ -7,6 +7,7 @@ import (
 	"flag"
 	"fmt"
 	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/ava-labs/avalanchego/tests/fixture/tmpnet"
@@ -29,9 +30,26 @@ type FlagVars struct {
 }
 
 func (v *FlagVars) AvalancheGoExecPath() string {
+	v.validateAvalancheGoExecPath()
 	return v.avalancheGoExecPath
 }
 
+func (v *FlagVars) validateAvalancheGoExecPath() {
+	if !filepath.IsAbs(v.avalancheGoExecPath) {
+		absPath, err := filepath.Abs(v.avalancheGoExecPath)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "avalanchego-path (%s) is a relative path but its absolute path cannot be determined: %v\n",
+				v.avalancheGoExecPath, err)
+		}
+
+		// If the absolute path file doesn't exist, it means it won't work out of the box.
+		if _, err := os.Stat(absPath); err != nil {
+			fmt.Fprintf(os.Stderr, "avalanchego-path (%s) is a relative path but must be an absolute path\n", v.avalancheGoExecPath)
+			os.Exit(2)
+		}
+	}
+}
+
 func (v *FlagVars) PluginDir() string {
 	return v.pluginDir
 }