add automated test verifying STDIN vs file-provided input

This adds a basic automated test verifying the validity of the issue #20
fix.

main_test.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+const (
+	testVersion    string = "test"
+	testExecutable string = "tf-summarize-test"
+)
+
+func TestMain(m *testing.M) {
+	// compile a 'tf-summarize' for use in running tests
+	exe := exec.Command("go", "build", "-ldflags", fmt.Sprintf("-X main.version=%s", testVersion), "-o", testExecutable)
+	err := exe.Run()
+	if err != nil {
+		os.Exit(1)
+	}
+
+	m.Run()
+
+	// delete the compiled tf-summarize
+	err = os.Remove(testExecutable)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func TestVersionArg(t *testing.T) {
+	args := []string{
+		"-v",
+	}
+
+	for _, arg := range args {
+		t.Run(fmt.Sprintf("when tf-summarize is passed '%s'", arg), func(t *testing.T) {
+			output, err := exec.Command(fmt.Sprintf("./%s", testExecutable), arg).CombinedOutput()
+			if err != nil {
+				t.Errorf("expected '%s' not to cause error; got '%v'", arg, err)
+			}
+
+			if !strings.Contains(string(output), testVersion) {
+				t.Errorf("expected '%s' to output version '%s'; got '%s'", arg, testVersion, output)
+			}
+		})
+	}
+}
+
+func TestTFSummarize(t *testing.T) {
+	tests := []struct {
+		command        string
+		expectedError  error
+		expectedOutput string
+	}{{
+		command:        fmt.Sprintf("./%s -md example/tfplan.json", testExecutable),
+		expectedOutput: "basic.txt",
+	}, {
+		command:        fmt.Sprintf("cat example/tfplan.json | ./%s -md", testExecutable),
+		expectedOutput: "basic.txt",
+	}}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("when tf-summarize is passed '%q'", test.command), func(t *testing.T) {
+			output, err := exec.Command("/bin/sh", "-c", test.command).CombinedOutput()
+			if err != nil && test.expectedError == nil {
+				t.Errorf("expected '%s' not to error; got '%v'", test.command, err)
+			}
+
+			b, err := os.ReadFile(fmt.Sprintf("testdata/%s", test.expectedOutput))
+			if err != nil {
+				t.Errorf("error reading file '%s': '%v'", test.expectedOutput, err)
+			}
+
+			expected := string(b)
+
+			if test.expectedError != nil && err == nil {
+				t.Errorf("expected error '%s'; got '%v'", test.expectedError.Error(), err)
+			}
+
+			if test.expectedError != nil && err != nil && test.expectedError.Error() != err.Error() {
+				t.Errorf("expected error '%s'; got '%v'", test.expectedError.Error(), err.Error())
+			}
+
+			if string(output) != expected {
+				t.Logf("expected output: \n%s", expected)
+				t.Logf("got output: \n%s", output)
+				t.Errorf("received unexpected output from '%s'", test.command)
+			}
+		})
+	}
+}

testdata/basic.txt

@@ -0,0 +1,9 @@
+| CHANGE |                                RESOURCE                                |
+|--------|------------------------------------------------------------------------|
+| add    | `github_repository.terraform_plan_summary`                             |
+|        | `module.github["demo-repository"].github_branch.development`           |
+|        | `module.github["demo-repository"].github_branch.main`                  |
+|        | `module.github["demo-repository"].github_repository.repository`        |
+|        | `module.github["terraform-plan-summary"].github_branch.development`    |
+|        | `module.github["terraform-plan-summary"].github_branch.main`           |
+|        | `module.github["terraform-plan-summary"].github_repository.repository` |