Update testify dep. version and clarify use of go get (#145)

diff --git a/README.md b/README.md
index 83e6627..92a53e1 100644
--- a/README.md
+++ b/README.md
@@ -73,7 +73,7 @@
 
 Open a terminal, change into the project directory and use the following command to run the unit tests:
 
-```
+```sh
 $ go test -v ./... -tags=unit
 ```
 
@@ -177,7 +177,7 @@
 }
 ```
 
-Then run it with the go tool:
+Then run it with the `go` tool:
 
 ```
 $ cd example
@@ -218,3 +218,30 @@
 
 > Be sure to [Sync your fork](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/syncing-a-fork) before starting any contributions to keep it up-to-date with the upstream repository.
 
+### Adding new dependencies
+
+Please use `go get` to add new dependencies to the `go.mod` file:
+
+```sh
+go get -u github.com/project/libname@v1.2.0
+```
+
+> Please avoid using commit hashes for referencing non-OpenWhisk libraries.
+
+### Updating dependency versions
+
+Although you might be tempted to edit the go.mod file directly, please use the recommended method of using the `go get` command:
+
+```sh
+go get -u github.com/project/libname  # Using "latest" version
+go get -u github.com/project/libname@v1.1.0 # Using tagged version
+go get -u github.com/project/libname@aee5cab1c  # Using a commit hash
+```
+
+### Updating Go version
+
+Although you could edit the version directly in the go.mod file, it is better to use the `go edit` command:
+
+```sh
+go mod edit -go=1.15
+```
diff --git a/go.mod b/go.mod
index cbbbd42..867db3c 100644
--- a/go.mod
+++ b/go.mod
@@ -13,5 +13,7 @@
 	github.com/onsi/ginkgo v1.15.0 // indirect
 	github.com/onsi/gomega v1.10.5 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
-	github.com/stretchr/testify v1.3.1-0.20190109162356-363ebb24d041
+	github.com/stretchr/objx v0.3.0 // indirect
+	github.com/stretchr/testify v1.6.1
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
 )
diff --git a/go.sum b/go.sum
index d1c04f6..25fcb1b 100644
--- a/go.sum
+++ b/go.sum
@@ -3,6 +3,7 @@
 github.com/cloudfoundry/jibber_jabber v0.0.0-20151120183258-bcc4c8345a21 h1:tuijfIjZyjZaHq9xDUh0tNitwXshJpbLkqMOJv4H3do=
 github.com/cloudfoundry/jibber_jabber v0.0.0-20151120183258-bcc4c8345a21/go.mod h1:po7NpZ/QiTKzBKyrsEAxwnTamCoh8uDk/egRpQ7siIc=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1VwoXQT9A3Wy9MM3WgvqSxFWenqJduM=
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/fatih/color v1.10.0 h1:s36xzo75JdqLaaWoiEHk767eHiwo0598uUxyfiPkDsg=
@@ -48,9 +49,15 @@
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.3.0 h1:NGXK3lHquSN08v5vWalVI/L8XU9hdzE/G6xsrze47As=
+github.com/stretchr/objx v0.3.0/go.mod h1:qt09Ya8vawLte6SNmTgCsAVtYtaKzEcn8ATUoHMkEqE=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.3.1-0.20190109162356-363ebb24d041 h1:/8BeG8ppzttbNYq43j+0izFSyhj3rXBQIQQTju6WC/I=
 github.com/stretchr/testify v1.3.1-0.20190109162356-363ebb24d041/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
+github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
@@ -107,3 +114,7 @@
 gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.3.0 h1:clyUAQHOM3G0M3f5vQj7LuJrETvjVot3Z5el9nffUtU=
 gopkg.in/yaml.v2 v2.3.0/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=