feat: implement case function (#16)

Follow GitHub Actions

* added unit tests

Closes #15

Reviewed-on: https://gitea.com/actions-oss/act-cli/pulls/16
Co-authored-by: ChristopherHX <christopher.homberger@web.de>
Co-committed-by: ChristopherHX <christopher.homberger@web.de>

pkg/schema/schema_test.go

@@ -148,3 +148,78 @@ jobs:
 	}).UnmarshalYAML(&node)
 	assert.NoError(t, err)
 }
+
+func TestSchemaErrors(t *testing.T) {
+	table := []struct {
+		name  string // test name
+		input string // workflow yaml input
+		err   string // error message substring
+	}{
+		{
+			name: "case even parameters is error",
+			input: `
+${{ 'on' }}: push
+jobs:
+    job-with-condition:
+        runs-on: self-hosted
+        steps:
+        - run: echo ${{ case(1 == 1, 'zero', 2 == 2, 'one', 'two', '') }}
+`,
+			err: "expected odd number of parameters for case got 6",
+		},
+		{
+			name: "case odd parameters no error",
+			input: `
+${{ 'on' }}: push
+jobs:
+    job-with-condition:
+        runs-on: self-hosted
+        steps:
+        - run: echo ${{ case(1 == 1, 'zero', 2 == 2, 'one', 'two') }}
+`,
+		},
+		{
+			name: "case 1 parameters error",
+			input: `
+${{ 'on' }}: push
+jobs:
+    job-with-condition:
+        runs-on: self-hosted
+        steps:
+        - run: echo ${{ case(1 == 1) }}
+`,
+			err: "missing parameters for case expected >= 3 got 1",
+		},
+		{
+			name: "invalid expression in step uses",
+			input: `
+on: push
+jobs:
+    job-with-condition:
+        runs-on: self-hosted
+        steps:
+        - uses: ${{ format('actions/checkout@v%s', 'v2') }}
+`,
+			err: "Line: 7 Column 17: expressions are not allowed here",
+		},
+	}
+
+	for _, test := range table {
+		t.Run(test.name, func(t *testing.T) {
+			var node yaml.Node
+			err := yaml.Unmarshal([]byte(test.input), &node)
+			if !assert.NoError(t, err) {
+				return
+			}
+			err = (&Node{
+				Definition: "workflow-root-strict",
+				Schema:     GetWorkflowSchema(),
+			}).UnmarshalYAML(&node)
+			if test.err != "" {
+				assert.ErrorContains(t, err, test.err)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}