feat(github): add IsPushable function and tests

Added a new function IsPushable to check if a user has push permissions
based on the viewerPermission API query.

Added new util file in the github package to include helper functions
and facilitate unit testing on command outputs.

internal/github/github.go

@@ -170,6 +170,15 @@ func (r *RealGitHub) GetPR(output io.Writer, workingDir string, branchName strin
 	return nil, &NoPRFoundError{Path: workingDir, BranchName: branchName}
 }
 
+func (r *RealGitHub) IsPushable(output io.Writer, workingDir string, fullRepoName string) (bool, error) {
+	s, err := execInstance.ExecuteAndCapture(output, workingDir, "gh", "repo", "view", fullRepoName, "--json", "viewerPermission")
+	if err != nil {
+		return false, err
+	}
+
+	return IsPushable(s)
+}
+
 func NewRealGitHub() *RealGitHub {
 	return &RealGitHub{}
 }

internal/github/util.go

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2021 Skyscanner Limited.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// util contains helper functions needed for both real and fake implementations of the GitHub interface
+
+package github
+
+import "encoding/json"
+
+type ViewerPermission struct {
+	ViewerPermission string `json:"viewerPermission"`
+}
+
+// IsPushable checks the output of the viewerPermission API query
+// and returns true if the user has write, maintain or admin permissions
+
+func IsPushable(viewerPermissionOutput string) (bool, error) {
+	var vp ViewerPermission
+
+	if err := json.Unmarshal([]byte(viewerPermissionOutput), &vp); err != nil {
+		return false, err
+	}
+
+	switch vp.ViewerPermission {
+	case "WRITE", "MAINTAIN", "ADMIN":
+		return true, nil
+	default:
+		return false, nil
+	}
+}

internal/github/util_test.go

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2021 Skyscanner Limited.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package github
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIsPushableReturnsTrueForAllCases(t *testing.T) {
+	testCases := []string{
+		`{"viewerPermission":"WRITE"}`,
+		`{"viewerPermission":"MAINTAIN"}`,
+		`{"viewerPermission":"ADMIN"}`,
+	}
+
+	for _, testCase := range testCases {
+		pushable, err := IsPushable(testCase)
+		assert.NoError(t, err)
+		assert.True(t, pushable)
+	}
+}
+
+func TestIsPushableReturnsFalseForUnknownPermission(t *testing.T) {
+	testCases := []string{
+		`{"viewerPermission":"UNKNOWN"}`,
+		`{"viewerPermission":"READ"}`,
+		`{"viewerPermission":"RANDOM"}`,
+		`{"viewerPermission":""}`,
+	}
+
+	for _, testCase := range testCases {
+		pushable, err := IsPushable(testCase)
+		assert.NoError(t, err)
+		assert.False(t, pushable)
+	}
+}
+
+func TestIsPushableReturnsErrorForInvalidJSON(t *testing.T) {
+	testCases := []string{
+		`{"anotherParam":"WRITE"`,     // valid JSON but not the expected format
+		`{"viewerPermission":"WRITE"`, // invalid JSON
+		`viewerPermission: WRITE`,     // invalid JSON
+		`{"viewerPermission": WRITE}`, // invalid JSON
+	}
+
+	for _, testCase := range testCases {
+		_, err := IsPushable(testCase)
+		assert.Error(t, err)
+	}
+}