Making your tests fail - Introduction to Mutation Testing

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MUTATION TESTING WITHSTANDING THE EPIDEMIC @felix_codes felixwu.dev

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http://bit.ly/flxwu-mutation-testing @felix_codes felixwu.dev

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http://bit.ly/flxwu-mutation-testing @felix_codes felixwu.dev

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@felix_codes

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@felix_codes WHY TESTS?

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@felix_codes WHY TESTS? “Quality is never an accident; it is always the result of intelligent effort.” John Ruskin

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@felix_codes FUNCTIONALITY WHY TESTS?

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@felix_codes CODE HOTSPOTS WHY TESTS?

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@felix_codes CODE HOTSPOTS WHY TESTS?

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@felix_codes STAYING AT THE TOP WHY TESTS?

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@felix_codes WHY TESTS? Engineers are responsible for finding errors in your product, not your user.

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@felix_codes WHY TESTS? Designers are responsible for finding errors in your product, not your user.

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@felix_codes WHY TESTS? PMs are responsible for finding errors in your product, not your user.

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@felix_codes WHY TESTS? You are responsible for finding errors in your product, not your user.

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@felix_codes WRITING GOOD TESTS WHY TESTS?

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@felix_codes WRITING GOOD TESTS WHY TESTS?

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@felix_codes TEST QUALITY WRITING GOOD TESTS WHY TESTS?

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@felix_codes MEASURING TEST QUALITY WHY TESTS?

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@felix_codes MEASURING TEST QUALITY 63% 1. WHY TESTS?

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@felix_codes MEASURING TEST QUALITY 63% 1. 2. WHY TESTS?

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@felix_codes MEASURING TEST QUALITY 63% 1. 2. Integration Unit End2End 3. WHY TESTS?

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@felix_codes CODE COVERAGE WHY TESTS?

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@felix_codes CODE COVERAGE WHY TESTS?

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@felix_codes CODE COVERAGE 72% WHY TESTS?

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@felix_codes COVERAGE REPORTS 72% CODE COVERAGE

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@felix_codes CODE COVERAGE TOOLS Corbetura JCov JaCoCo Istanbul Blanket.js Jest CODE COVERAGE

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@felix_codes COVERAGE vs. MAINTAINABILITY Maintainability Code coverage IDEAL CODE COVERAGE

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@felix_codes Maintainability Code coverage DANGER ZONE CODE COVERAGE COVERAGE vs. MAINTAINABILITY

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@felix_codes Maintainability Code coverage REALITY CODE COVERAGE COVERAGE vs. MAINTAINABILITY

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@felix_codes Quality Quantity DANGER ZONE CODE COVERAGE QUANTITY vs. QUALITY

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@felix_codes Quality Quantity CODE COVERAGE QUANTITY vs. QUALITY 85%

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@felix_codes Quality Quantity CODE COVERAGE QUANTITY vs. QUALITY 85% 100%

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@felix_codes Quality Quantity CODE COVERAGE QUANTITY vs. QUALITY 85% 100% you get what you measure!

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@felix_codes CODE COVERAGE Code coverage is not the best indicator for test strength and thoroughness

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@felix_codes CODE COVERAGE Code coverage is not the best indicator for test strength and thoroughness ?

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@felix_codes CODE COVERAGE We are in need of an effective measurement of our tests quality

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@felix_codes MUTATION TESTING

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@felix_codes WHAT WHY HOW

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@felix_codes WHAT “Making your test cases fail”

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 1.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 1.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 2.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 2.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 2.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 2.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 2.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 3.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 3.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 3.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 3.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 3.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING 3.

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING STEPS OF MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING We can assess the quality of the test cases which should be robust enough to fail mutant code.

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING

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@felix_codes WHAT IS MUTATION TESTING MUTATION EXAMPLE

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@felix_codes MUTATION TESTING EXAMPLE GVODUJPODBO7JFX%PDVNFOU VTFS \ SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ ^

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ ^ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ ^ 2 3 1 4 SFUVSOUSVF SFUVSOGBMTF SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 1 SFUVSOUSVF !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 1 SFUVSOUSVF !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 1 SFUVSOUSVF !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 2 SFUVSOGBMTF !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 2 SFUVSOGBMTF !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 2 SFUVSOGBMTF !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 3 SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 3 SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 3 SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 4 SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 4 SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ ^ 4 SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes 2 3 SFUVSOUSVF SFUVSOGBMTF SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ MUTATION TESTING EXAMPLE

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@felix_codes 2 3 SFUVSOGBMTF SFUVSO VTFSQFSNJTTJPO)JFSBSDIZ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ ^ MUTATION TESTING EXAMPLE

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@felix_codes 2 3 SFUVSOGBMTF SFUVSO VTFSQFSNJTTJPO)JFSBSDIZ QVCMJDCPPMFBODBO7JFX%PDVNFOU 6TFSVTFS \ SFUVSOVTFSQFSNJTTJPO)JFSBSDIZ ^ !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ BTTFSU&RVBMT USVF DBO7JFX%PDVNFOU OFX6TFS BTTFSU&RVBMT USVF DBO7JFX%PDVNFOU OFX6TFS MUTATION TESTING EXAMPLE

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@felix_codes !5FTU QVCMJDWPJEUFTU7JFX%PDVNFOU \ BTTFSU&RVBMT GBMTF DBO7JFX%PDVNFOU OFX6TFS ^ BTTFSU&RVBMT USVF DBO7JFX%PDVNFOU OFX6TFS BTTFSU&RVBMT USVF DBO7JFX%PDVNFOU OFX6TFS MUTATION TESTING EXAMPLE

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@felix_codes MUTANTS “Humans are mutants, everything's a mutant - things that evolve.” Oscar Isaac

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@felix_codes

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@felix_codes Mutants simulate human programming errors

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@felix_codes MUTANTS TYPES OF MUTANTS

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@felix_codes MUTANTS TYPES OF MUTANTS Value mutation

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@felix_codes MUTANTS TYPES OF MUTANTS Value mutation Operator mutation

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@felix_codes MUTANTS TYPES OF MUTANTS Value mutation Operator mutation Statement mutation

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@felix_codes MUTANTS TYPES OF MUTANTS Value mutation Operator mutation Statement mutation int a = 12 int a = 15

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@felix_codes MUTANTS TYPES OF MUTANTS Value mutation Operator mutation Statement mutation a++; a++; a++; int a = 12 int a = 15

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@felix_codes MUTANTS TYPES OF MUTANTS Value mutation Operator mutation Statement mutation

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@felix_codes MUTANTS TYPES OF MUTANTS Arithmetic Relational Conditional a + b a - b while(a < b) while(true) if(a || b) if (a && b) Operator mutation

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@felix_codes MUTANTS

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@felix_codes Mutants simulate human programming errors MUTANTS

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@felix_codes Mutants simulate errors of competent programmers “ ” MUTANTS

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@felix_codes Mutants simulate errors of competent programmers if (age > 18) // check if adult “ ” MUTANTS

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@felix_codes Mutants simulate errors of competent programmers if (age > 18) // check if adult “ ” MUTANTS

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@felix_codes Mutants simulate minor errors of competent programmers. Major flaws always arise from minor errors because of the coupling effect. “ ” MUTANTS

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@felix_codes MUTANTS

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@felix_codes Mutation Testing score number of mutants killed total mutants amount 0% MUTANTS

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@felix_codes WHAT WHY HOW

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@felix_codes HOW

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@felix_codes WHAT WHY HOW

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@felix_codes WHY

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@felix_codes WHY MUTATION TESTING? PITFALLS

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@felix_codes WHY MUTATION TESTING? PITFALLS “Equivalent mutants” =

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@felix_codes WHY MUTATION TESTING? PITFALLS JOUNBY JOU<>WBMVFT \ JOUS J S GPS JJWBMVFTMFOHUIJ \ JG WBMVFTWBMVFT SJ ^ SFUVSOWBMVFT ^

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@felix_codes WHY MUTATION TESTING? PITFALLS JOUNBY JOU<>WBMVFT \ JOUS J S GPS JJWBMVFTMFOHUIJ \ JG WBMVFTWBMVFT SJ ^ SFUVSOWBMVFT ^ JOUNBY JOU<>WBMVFT \ JOUS J S GPS JJWBMVFTMFOHUIJ \ JG WBMVFTWBMVFT SJ ^ SFUVSOWBMVFT ^

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@felix_codes WHY MUTATION TESTING? PITFALLS

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@felix_codes WHY MUTATION TESTING? PITFALLS “Equivalent mutants” =

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@felix_codes WHY MUTATION TESTING? PEOPLE ARE REALIZING

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@felix_codes WHY MUTATION TESTING? BENEFITS Maintainability Code coverage DANGER ZONE

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@felix_codes WHY MUTATION TESTING? BENEFITS Maintainability Code coverage IDEAL

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@felix_codes WHY MUTATION TESTING? BENEFITS Maintainability Code coverage IDEAL

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@felix_codes WHY MUTATION TESTING? CONTINIOUS INTEGRATION

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@felix_codes WHAT IS MUTATION TESTING Aaltonen, Kalle & Ihantola, Petri & Seppälä, Otto. (2015); Mutation Testing vs. Code Coverage in automated assessment

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@felix_codes WHAT IS MUTATION TESTING Aaltonen, Kalle & Ihantola, Petri & Seppälä, Otto. (2015); Mutation Testing vs. Code Coverage in automated assessment

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@felix_codes WHAT IS MUTATION TESTING Aaltonen, Kalle & Ihantola, Petri & Seppälä, Otto. (2015); Mutation Testing vs. Code Coverage in automated assessment

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WITHSTANDING THE EPIDEMIC Felix Wu - @felix_codes MUTATION TESTING

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Felix Wu - @felix_codes PITest(Java) Javalanche(Java) Stryker(JS) http://bit.ly/flxwu-mutation-testing