Merge branch 'docs/add-go-test-guidelines' into 'master'

Add Go test guidelines

See merge request gitlab-org/gitlab-ce!29159

doc/development/go_guide/index.md

@@ -173,6 +173,45 @@ func Test(t *testing.T) {
 }
 ```
 
+### Table-Driven Tests
+
+Using [Table-Driven Tests](https://github.com/golang/go/wiki/TableDrivenTests)
+is generally good practice when you have multiple entries of
+inputs/outputs for the same function. Below are some guidelines one can
+follow when writing table-driven test. These guidelines are mostly
+extracted from Go standard library source code. Keep in mind it's OK not
+to follow these guidelines when it makes sense.
+
+#### Defining test cases
+
+Each table entry is a complete test case with inputs and expected
+results, and sometimes with additional information such as a test name
+to make the test output easily readable.
+
+- [Define a slice of anonymous struct](https://github.com/golang/go/blob/50bd1c4d4eb4fac8ddeb5f063c099daccfb71b26/src/encoding/csv/reader_test.go#L16)
+  inside of the test.
+- [Define a slice of anonymous struct](https://github.com/golang/go/blob/55d31e16c12c38d36811bdee65ac1f7772148250/src/cmd/go/internal/module/module_test.go#L9-L66)
+  outside of the test.
+- [Named structs](https://github.com/golang/go/blob/2e0cd2aef5924e48e1ceb74e3d52e76c56dd34cc/src/cmd/go/internal/modfetch/coderepo_test.go#L54-L69)
+  for code reuse.
+- [Using `map[string]struct{}`](https://github.com/golang/go/blob/6d5caf38e37bf9aeba3291f1f0b0081f934b1187/src/cmd/trace/annotations_test.go#L180-L235).
+
+#### Contents of the test case
+
+- Ideally, each test case should have a field with a unique identifier
+  to use for naming subtests. In the Go standard library, this is commonly the
+  `name string` field.
+- Use `want`/`expect`/`actual` when you are specifcing something in the
+  test case that will be used for assertion.
+
+#### Variable names
+
+- Each table-driven test map/slice of struct can be named `tests`.
+- When looping through `tests` the anonymous struct can be referred
+  to as `tt` or `tc`.
+- The description of the test can be referred to as
+  `name`/`testName`/`tn`.
+
 ### Benchmarks
 
 Programs handling a lot of IO or complex operations should always include