Edge Case Catalog

Edge Case Catalog

Use this catalog as a learner checklist after each lesson. The answer verifier automates these checks, but reading the cases first helps you understand what can go wrong.

Lesson 1: Pricing And OOP Rules

• Empty cart subtotal is 0.
• Empty cart has no most-expensive item.
• Quantity matters: line total is unit price times quantity.
• Item count means sum of quantities, not number of cart lines.
• Discount 0 preserves subtotal.
• Discount 100 returns zero.
• Discount below 0 is invalid.
• Discount above 100 is invalid.
• Tax uses basis points, so 825 means 8.25%.
• Tax rounds to the nearest cent.
• Shipping is free when subtotal equals the free-shipping threshold.
• Empty carts ship for 0.
• Negative shipping threshold is invalid.
• Negative standard shipping price is invalid.
• Sorting by line total breaks ties by name.
• Duplicate item names merge quantities.

Lesson 2: Decorator Rules

• Prefix changes the message before delegation.
• Suffix changes the message before delegation.
• Message transform can trim, uppercase, redact, or normalize.
• Rate-limit note changes the result after delegation.
• Audit records the message at the point where the audit wrapper sits.
• Blocklist short-circuits and does not delegate.
• Truncation accepts max length 0.
• Truncation rejects negative length.
• Counting records every send attempt that reaches the counting wrapper.
• Counting outside blocklist and counting inside blocklist produce different counts.
• Composition with an empty decorator list returns the base channel.
• Composition order determines which wrapper is outermost.

Lesson 3: Concurrency And Aggregation Rules

• Parallel word count must match sequential word count.
• Empty input returns an empty count map.
• Blank documents contribute no words.
• Punctuation separates tokens.
• Case differences normalize to lowercase.
• thread should not match threads.
• Merge functions should not mutate input maps.
• Overlapping keys add counts.
• Top word on an empty map has no result.
• Top-N with limit 0 returns an empty list.
• Top-N with negative limit is invalid.
• Top-N ties break alphabetically.
• Stop words are case-insensitive.
• Ordered parallel document lengths preserve input order.
• Interrupted tasks should restore the interrupt flag before throwing.

Lesson 4: Image And Pixel Rules

• Clamp handles lower bound, upper bound, and equal bounds.
• Invalid clamp range is rejected.
• Gray values must be bytes in 0..255.
• Inverting black returns white.
• Inverting white returns black.
• Threshold includes values equal to cutoff.
• Threshold rejects invalid cutoff values.
• Luma extracts packed red, green, and blue channels.
• Packed gray output is opaque ARGB.
• Normalization clamps below and above range.
• Normalization rejects min >= max.
• Blend accepts alpha 0 and 1.
• Blend rejects alpha outside 0..1.
• Sobel magnitude clamps high gradient values.
• Image sampling clamps outside coordinates to the nearest edge.
• Empty images are invalid.
• Ragged images are invalid.
• mean3x3 uses clamped boundary samples at corners.

Lesson 5: Java @ Annotation Rules

• @Override is compiler-checked and should fail if the method does not override anything.
• @FunctionalInterface checks that exactly one abstract method exists.
• @Deprecated can expose since and forRemoval metadata.
• @SuppressWarnings should be scoped narrowly.
• @SafeVarargs belongs only on safe final, static, or private varargs methods or constructors.
• @Retention(RUNTIME) is required for normal runtime reflection.
• @Retention(CLASS) is not normally visible through reflection.
• @Target controls legal annotation placement.
• @Repeatable annotations should be read with getAnnotationsByType.
• @Inherited works for class annotations, not method annotations.
• @Target(TYPE_USE) is read through annotated types, not ordinary parameter annotations.
• Package annotations live in package-info.java.
• Record component annotations are read from RecordComponent.
• Type parameter annotations are read from Class.getTypeParameters.
• Decorator/interceptor annotations are metadata until a framework or runtime code interprets them.
• Getter/setter annotations such as Lombok-style @Getter and @Setter require an annotation processor or framework to generate behavior; this repo models them as metadata only.
• Source-only annotations such as local markers, @Serial, and @Native can affect tools or compiler checks without being runtime behavior.

Lesson 6: Spring Boot Hello World Rules

• Missing name uses the configured default name.
• Blank or whitespace-only name uses the configured default name.
• Leading and trailing spaces are trimmed.
• Repeated internal whitespace collapses to a single space.
• Names longer than tutorial.greeting.max-name-length are rejected.
• Missing punctuation uses !.
• Blank punctuation uses !.
• Allowed punctuation is only !, ?, or ..
• URL-encoded ? must be handled as punctuation, not as a query separator.
• Unsupported punctuation returns HTTP 400 through ApiExceptionHandler.
• GET /hello and POST /hello use the same service rules.
• JSON record fields should be message, name, and punctuation.
• Controller tests should verify both HTTP status and response body.
• The app should bind to 0.0.0.0:8080 by default when served locally.