Test the remaining CLI cases (closes #16)

Most of the command-line contract was already tested through run. This
adds what was missing: report and trees with no database exit 1 with
the message telling the user to run scan; a scan that skips an
unreadable file prints its warning and counts the skip in its summary;
the report and trees summary lines are checked exactly. The fatal-path
test now takes its subcommands from the command tree, so a new
subcommand wired without runE fails it. The nonexistent-operand test
gets an accurate name.

Model: opus-5-5

TODO.md

@@ -29,6 +29,10 @@
 
 # Completed Steps
 
+- tests cover a missing database, the `scan` skip warning, the `report`
+  and `trees` summary lines, and every subcommand going through `runE`
+  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/16)
+
 - `.golangci.yml` replaced with the current canonical copy, which uses
   `gomodguard_v2`, so lint no longer prints a deprecation warning
   (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/26)

main_test.go

@@ -85,8 +85,9 @@ func makeReadOnly(t *testing.T, path string) {
 
 // captureStderr redirects os.Stderr to a file for the rest of the test
 // and returns a function reading back everything written to it. scan
-// writes its warnings and summary straight to os.Stderr, not to the
+// writes its warnings and summary, and report and trees their
-// stderr writer run is given.
+// summaries, straight to os.Stderr, not to the stderr writer run is
+// given.
 func captureStderr(t *testing.T) func() string {
 	t.Helper()
 
@@ -184,17 +185,18 @@ func TestRunFatalAfterOpenClosesDatabase(t *testing.T) {
 	// sidecar check is evidence of the close only for scan: report and
 	// trees only read a database that is out of WAL mode, which leaves
 	// nothing on disk whether they close it or not.
-	cases := map[string][]string{
+	//
-		cmdScan:   {cmdScan},
+	// The subcommands come from the command tree, so a new one is
-		cmdReport: {cmdReport},
+	// checked too: one wired with a bare RunE instead of runE reports
-		cmdTrees:  {cmdTrees},
+	// its failure as a usage error, exit 2 with the usage text.
-	}
+	for _, cmd := range newRootCommand(io.Discard, io.Discard).Commands() {
+		name := cmd.Name()
 
-	for name, args := range cases {
 		t.Run(name, func(t *testing.T) {
 			path := brokenDatabase(t)
 			t.Setenv(databaseEnv, path)
 
+			args := []string{name}
 			if name == cmdScan {
 				args = append(args, t.TempDir())
 			}
@@ -219,7 +221,7 @@ func TestRunFatalAfterOpenClosesDatabase(t *testing.T) {
 	}
 }
 
-func TestRunMissingOperandIsFatalNotUsage(t *testing.T) {
+func TestRunNonexistentPathIsFatalNotUsage(t *testing.T) {
 	// README §Error handling: a PATH operand that does not exist is a
 	// fatal error (1), not a usage error (2) — and a runtime failure
 	// must not dump the usage text.
@@ -258,6 +260,34 @@ func assertFatalOutput(t *testing.T, stderr, stdout string) {
 	}
 }
 
+func TestRunMissingDatabaseIsFatal(t *testing.T) {
+	// README §Database: report and trees need an existing database; a
+	// missing one exits 1 with a message telling the user to run scan.
+	for _, name := range []string{cmdReport, cmdTrees} {
+		t.Run(name, func(t *testing.T) {
+			path := testDBPath(t)
+			t.Setenv(databaseEnv, path)
+
+			var stdout, stderr bytes.Buffer
+
+			code := run([]string{name}, &stdout, &stderr)
+			if code != exitFatal {
+				t.Errorf("run(%s) = %d, want %d", name, code, exitFatal)
+			}
+
+			want := "sfdupes: " + path + ": no database (run \"sfdupes " +
+				"scan\" first, or set " + databaseEnv + ")\n"
+			if got := stderr.String(); got != want {
+				t.Errorf("stderr = %q, want %q", got, want)
+			}
+
+			if got := stdout.String(); got != "" {
+				t.Errorf("stdout = %q, want nothing (data only)", got)
+			}
+		})
+	}
+}
+
 func TestRunUsageErrors(t *testing.T) {
 	// Usage errors keep exiting 2 with cobra's own report on stderr.
 	cases := map[string]struct {
@@ -453,10 +483,41 @@ func scanOK(t *testing.T, operands ...string) string {
 }
 
 func TestRunScanSucceedsDespiteWarnings(t *testing.T) {
+	// README §Error handling: a scan that skips a file it cannot read
+	// warns, counts the skip in its summary, and still exits 0, which
+	// scanOK checks along with the empty stdout.
+	if os.Geteuid() == 0 {
+		t.Skip("root ignores file permissions")
+	}
+
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	scanFixture(t)
+	dir := t.TempDir()
+	writeFile(t, dir, "a.bin", pattern(1, 300))
+
+	// Same size as a.bin, so the scan reads it, and the read fails.
+	unreadable := writeFile(t, dir, "unreadable.bin", pattern(2, 300))
+
+	err := os.Chmod(unreadable, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	stderr := scanOK(t, dir)
+
+	warning := "hash " + unreadable + ": open " + unreadable +
+		": permission denied\n"
+	if !strings.Contains(stderr, warning) {
+		t.Errorf("stderr = %q, want %q", stderr, warning)
+	}
+
+	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+		"0 unchanged), 1 skipped\n"
+	if !strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q", stderr, summary)
+	}
+
 	assertNoSidecars(t, path)
 }
 
@@ -563,12 +624,14 @@ func TestRunReportSucceeds(t *testing.T) {
 
 	dupes := scanFixture(t)
 
-	var stdout, stderr bytes.Buffer
+	var stdout bytes.Buffer
 
-	code := run([]string{cmdReport}, &stdout, &stderr)
+	stderr := captureStderr(t)
+
+	code := run([]string{cmdReport}, &stdout, os.Stderr)
 	if code != exitOK {
 		t.Fatalf("run(report) = %d, want %d; stderr: %s",
-			code, exitOK, stderr.String())
+			code, exitOK, stderr())
 	}
 
 	want := "first\tdupe\tsize\n" + dupes[0] + "\t" + dupes[1] + "\t300\n"
@@ -576,6 +639,12 @@ func TestRunReportSucceeds(t *testing.T) {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
 
+	want = "report: 2 records read, 1 duplicate groups, 1 dupe files, " +
+		"300 B reclaimable\n"
+	if got := stderr(); got != want {
+		t.Errorf("stderr = %q, want %q", got, want)
+	}
+
 	assertNoSidecars(t, path)
 }
 
@@ -585,12 +654,14 @@ func TestRunTreesSucceeds(t *testing.T) {
 
 	dupes := scanFixture(t)
 
-	var stdout, stderr bytes.Buffer
+	var stdout bytes.Buffer
 
-	code := run([]string{cmdTrees}, &stdout, &stderr)
+	stderr := captureStderr(t)
+
+	code := run([]string{cmdTrees}, &stdout, os.Stderr)
 	if code != exitOK {
 		t.Fatalf("run(trees) = %d, want %d; stderr: %s",
-			code, exitOK, stderr.String())
+			code, exitOK, stderr())
 	}
 
 	// The two directories holding the duplicate pair are duplicate
@@ -601,6 +672,12 @@ func TestRunTreesSucceeds(t *testing.T) {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
 
+	want = "trees: 2 records read, 1 duplicate tree groups, 1 dupe trees, " +
+		"300 B reclaimable\n"
+	if got := stderr(); got != want {
+		t.Errorf("stderr = %q, want %q", got, want)
+	}
+
 	assertNoSidecars(t, path)
 }