Should be len(policy.Rules) instead of len.(policy.Rules)?

sed s/lenth/length

Please use more meaningful names, rather than s here.

Errors should not start with uppercase, so no audit...

Maybe change the error to: empty policy file is not allowed or similar.

Nit: I think something like policyCnt is better for readability than length

nit: glog messages shouldn't end in a \n (there is always an implicit newline).

please make this error message more precise, e.g. loaded illegal policy with 0 rules from file %s

Done, plz check ^_^

why this change?

disregard. This should be alpha.

Since this is a set of testCases for a specific function, it's better to move it inside this function

Sorry for not mentioning this earlier

I think for readability it's better to avoid manually writing '\n'. Maybe do something like this instead?

{
  "policyWithNoRule",
  `
apiVersion: audit.k8s.io/v1beta1
kind: Policy
`,
}

This part is a copy-paste from another test. Extract to a separate function maybe?

Smth like _, err := loadPolicyFromString(tc.policy)

Thx for review. but, LoadPolicyFromFile is the function what I'm testing in reader.go.

I don't mind that, you will have the call to that function in the code. But if you want to have it called explicitly in the code -- that's OK also, wrap the rest at least:

f, err := writePolicy(tc.policy)
require.NoError(t, err)
defer os.Remove(f)

_, err = LoadPolicyFromFile(f)

WriteString is a function imported from package "os"

func (f *File) WriteString(s string) (n int, err error)

maybe I can only change caseContent to policy?

WriteString is a function imported from package "os"

I don't understand how it makes extracting a function impossible. Could you please elaborate?

What I mean is doing the following:

func TestPolicyCntCheck(t *testing.T) {
	for _, tc := range testCases {
		f, err := writePolicy(tc.policy)
		require.NoError(t, err)
		defer os.Remove(f)

		_, err = LoadPolicyFromFile(f)
		assert.Errorf(t, err, "loaded illegal policy with 0 rules from testCase %s", tc.caseName)
	}
}

func writePolicy(policy string) (string, error) {
		...
}

And replace the same piece of code in TestParserV1beta1

Oh very sorry about that. I misunderstood what you meant just now.

This comment adds no new information => not needed

Small nit: usually *testing.T comes as a first argument

Thx for your careful instruction! I learned a lot.^_^