acc: Print replacements on error and rm duplicates (#2230)

## Changes
- File comparison files in acceptance test, print the contents of all
applied replacements. Do it once per test.
- Remove duplicate entries in replacement list.

## Tests
Manually, change out files of existing test, you'll get this printed
once, after first assertion:

```
        acceptance_test.go:307: Available replacements:
            REPL /Users/denis\.bilenko/work/cli/acceptance/build/databricks => $$CLI
            REPL /private/var/folders/5y/9kkdnjw91p11vsqwk0cvmk200000gp/T/TestAccept598522733/001 => $$TMPHOME
            ...
```

acceptance/acceptance_test.go

@@ -228,9 +228,11 @@ func runTest(t *testing.T, dir, coverDir string, repls testdiff.ReplacementsCont
 	formatOutput(out, err)
 	require.NoError(t, out.Close())
 
+	printedRepls := false
+
 	// Compare expected outputs
 	for relPath := range outputs {
-		doComparison(t, repls, dir, tmpDir, relPath)
+		doComparison(t, repls, dir, tmpDir, relPath, &printedRepls)
 	}
 
 	// Make sure there are not unaccounted for new files
@@ -245,12 +247,12 @@ func runTest(t *testing.T, dir, coverDir string, repls testdiff.ReplacementsCont
 		if strings.HasPrefix(relPath, "out") {
 			// We have a new file starting with "out"
 			// Show the contents & support overwrite mode for it:
-			doComparison(t, repls, dir, tmpDir, relPath)
+			doComparison(t, repls, dir, tmpDir, relPath, &printedRepls)
 		}
 	}
 }
 
-func doComparison(t *testing.T, repls testdiff.ReplacementsContext, dirRef, dirNew, relPath string) {
+func doComparison(t *testing.T, repls testdiff.ReplacementsContext, dirRef, dirNew, relPath string, printedRepls *bool) {
 	pathRef := filepath.Join(dirRef, relPath)
 	pathNew := filepath.Join(dirNew, relPath)
 	bufRef, okRef := readIfExists(t, pathRef)
@@ -295,6 +297,15 @@ func doComparison(t *testing.T, repls testdiff.ReplacementsContext, dirRef, dirN
 		t.Logf("Overwriting existing output file: %s", relPath)
 		testutil.WriteFile(t, pathRef, valueNew)
 	}
+
+	if !equal && printedRepls != nil && !*printedRepls {
+		*printedRepls = true
+		var items []string
+		for _, item := range repls.Repls {
+			items = append(items, fmt.Sprintf("REPL %s => %s", item.Old, item.New))
+		}
+		t.Log("Available replacements:\n" + strings.Join(items, "\n"))
+	}
 }
 
 // Returns combined script.prepare (root) + script.prepare (parent) + ... + script + ... + script.cleanup (parent) + ...

libs/testdiff/replacement.go

@@ -76,7 +76,11 @@ func (r *ReplacementsContext) Set(old, new string) {
 	if err == nil {
 		encodedOld, err := json.Marshal(old)
 		if err == nil {
-			r.appendLiteral(trimQuotes(string(encodedOld)), trimQuotes(string(encodedNew)))
+			encodedStrNew := trimQuotes(string(encodedNew))
+			encodedStrOld := trimQuotes(string(encodedOld))
+			if encodedStrNew != new || encodedStrOld != old {
+				r.appendLiteral(encodedStrOld, encodedStrNew)
+			}
 		}
 	}