allow convert to take stdin (#1570)

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

test/cli/convert_cmd_test.go

@@ -0,0 +1,50 @@
+package cli
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+func TestConvertCmd(t *testing.T) {
+	assertions := []traitAssertion{
+		assertInOutput("PackageName: musl-utils"),
+		assertSuccessfulReturnCode,
+	}
+
+	tests := []struct {
+		from string
+		to   string
+	}{
+		{from: "syft-json", to: "spdx-tag-value"},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("from %s to %s", test.from, test.to), func(t *testing.T) {
+			sbomArgs := []string{"dir:./test-fixtures/image-pkg-coverage", "-o", test.from}
+			cmd, stdout, stderr := runSyft(t, nil, sbomArgs...)
+			if cmd.ProcessState.ExitCode() != 0 {
+				t.Log("STDOUT:\n", stdout)
+				t.Log("STDERR:\n", stderr)
+				t.Log("COMMAND:", strings.Join(cmd.Args, " "))
+				t.Fatalf("failure executing syft creating an sbom")
+				return
+			}
+
+			convertArgs := []string{"convert", "-", "-o", test.to}
+			cmd = getSyftCommand(t, convertArgs...)
+
+			cmd.Stdin = strings.NewReader(stdout)
+			stdout, stderr = runCommandObj(t, cmd, nil, false)
+
+			for _, traitFn := range assertions {
+				traitFn(t, stdout, stderr, cmd.ProcessState.ExitCode())
+			}
+			if t.Failed() {
+				t.Log("STDOUT:\n", stdout)
+				t.Log("STDERR:\n", stderr)
+				t.Log("COMMAND:", strings.Join(cmd.Args, " "))
+			}
+		})
+	}
+}